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 $207.96   11.840%   $232.5825   $232.58   $232.60   $232.60  
  Purchase #2 $138.46   8.119%   $149.7016   $149.70   $149.70   $149.70  
  Purchase #3 $83.27   7.365%   $89.4028   $89.40   $89.40   $89.40  
  Purchase #4 $28.86   10.629%   $31.9275   $31.93   $31.95   $31.90  
  Purchase #5 $110.40   5.716%   $116.7105   $116.71   $116.70   $116.70  
  Purchase #6 $118.39   12.277%   $132.9247   $132.92   $132.90   $132.90  
  Purchase #7 $129.78   5.376%   $136.757   $136.76   $136.75   $136.80  
  7 purchase totals = $817.12       $890.0066   $890.00   $890.00   $890.00