Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $200.29   6.241%   $212.7901   $212.79   $212.80   $212.80  
  Purchase #2 $227.63   8.483%   $246.9399   $246.94   $246.95   $246.90  
  Purchase #3 $135.81   3.514%   $140.5824   $140.58   $140.60   $140.60  
  Purchase #4 $148.66   12.307%   $166.9556   $166.96   $166.95   $167.00  
  Purchase #5 $226.32   10.552%   $250.2013   $250.20   $250.20   $250.20  
  Purchase #6 $193.31   4.362%   $201.7422   $201.74   $201.75   $201.70  
  Purchase #7 $217.77   8.392%   $236.0453   $236.05   $236.05   $236.00  
  7 purchase totals = $1,349.79       $1,455.2568   $1,455.26   $1,455.30   $1,455.20