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 $51.97   13.438%   $58.9537   $58.95   $58.95   $59.00  
  Purchase #2 $55.42   7.200%   $59.4102   $59.41   $59.40   $59.40  
  Purchase #3 $154.80   7.494%   $166.4007   $166.40   $166.40   $166.40  
  Purchase #4 $249.76   8.667%   $271.4067   $271.41   $271.40   $271.40  
  Purchase #5 $52.53   3.858%   $54.5566   $54.56   $54.55   $54.60  
  Purchase #6 $214.96   8.295%   $232.7909   $232.79   $232.80   $232.80  
  Purchase #7 $171.29   10.192%   $188.7479   $188.75   $188.75   $188.70  
  7 purchase totals = $950.73       $1,032.2667   $1,032.27   $1,032.25   $1,032.30