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 $54.95   5.484%   $57.9635   $57.96   $57.95   $58.00  
  Purchase #2 $39.83   12.468%   $44.796   $44.80   $44.80   $44.80  
  Purchase #3 $197.49   9.143%   $215.5465   $215.55   $215.55   $215.50  
  Purchase #4 $69.97   7.633%   $75.3108   $75.31   $75.30   $75.30  
  Purchase #5 $103.56   8.731%   $112.6018   $112.60   $112.60   $112.60  
  Purchase #6 $236.70   8.387%   $256.552   $256.55   $256.55   $256.60  
  Purchase #7 $12.50   3.357%   $12.9196   $12.92   $12.90   $12.90  
  7 purchase totals = $715.00       $775.6902   $775.69   $775.65   $775.70