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 $91.73   4.704%   $96.045   $96.05   $96.05   $96.00  
  Purchase #2 $96.74   12.289%   $108.6284   $108.63   $108.65   $108.60  
  Purchase #3 $62.26   9.446%   $68.1411   $68.14   $68.15   $68.10  
  Purchase #4 $25.88   10.718%   $28.6538   $28.65   $28.65   $28.70  
  Purchase #5 $41.78   9.164%   $45.6087   $45.61   $45.60   $45.60  
  Purchase #6 $115.53   8.263%   $125.0762   $125.08   $125.10   $125.10  
  Purchase #7 $117.46   11.590%   $131.0736   $131.07   $131.05   $131.10  
  7 purchase totals = $551.38       $603.2268   $603.23   $603.25   $603.20