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 $58.73   9.821%   $64.4979   $64.50   $64.50   $64.50  
  Purchase #2 $190.78   5.677%   $201.6106   $201.61   $201.60   $201.60  
  Purchase #3 $27.93   10.637%   $30.9009   $30.90   $30.90   $30.90  
  Purchase #4 $177.91   12.614%   $200.3516   $200.35   $200.35   $200.40  
  Purchase #5 $150.99   9.731%   $165.6828   $165.68   $165.70   $165.70  
  Purchase #6 $83.81   4.644%   $87.7021   $87.70   $87.70   $87.70  
  Purchase #7 $151.67   10.747%   $167.97   $167.97   $167.95   $168.00  
  7 purchase totals = $841.82       $918.7159   $918.71   $918.70   $918.80