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 $58.47   12.204%   $65.6057   $65.61   $65.60   $65.60  
  Purchase #2 $158.88   12.299%   $178.4207   $178.42   $178.40   $178.40  
  Purchase #3 $159.77   4.291%   $166.6257   $166.63   $166.65   $166.60  
  Purchase #4 $216.69   11.614%   $241.8564   $241.86   $241.85   $241.90  
  Purchase #5 $136.80   9.620%   $149.9602   $149.96   $149.95   $150.00  
  Purchase #6 $68.70   11.351%   $76.4981   $76.50   $76.50   $76.50  
  Purchase #7 $25.96   10.268%   $28.6256   $28.63   $28.65   $28.60  
  7 purchase totals = $825.27       $907.5924   $907.61   $907.60   $907.60