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 $213.41   7.579%   $229.5843   $229.58   $229.60   $229.60  
  Purchase #2 $141.35   4.157%   $147.2259   $147.23   $147.25   $147.20  
  Purchase #3 $60.97   6.611%   $65.0007   $65.00   $65.00   $65.00  
  Purchase #4 $234.40   9.192%   $255.946   $255.95   $255.95   $255.90  
  Purchase #5 $170.53   5.370%   $179.6875   $179.69   $179.70   $179.70  
  Purchase #6 $188.94   10.379%   $208.5501   $208.55   $208.55   $208.60  
  Purchase #7 $129.67   9.447%   $141.9199   $141.92   $141.90   $141.90  
  7 purchase totals = $1,139.27       $1,227.9144   $1,227.92   $1,227.95   $1,227.90