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 $54.81   9.417%   $59.9715   $59.97   $59.95   $60.00  
  Purchase #2 $218.78   8.246%   $236.8206   $236.82   $236.80   $236.80  
  Purchase #3 $110.73   5.508%   $116.829   $116.83   $116.85   $116.80  
  Purchase #4 $152.80   7.735%   $164.6191   $164.62   $164.60   $164.60  
  Purchase #5 $85.30   10.519%   $94.2727   $94.27   $94.25   $94.30  
  Purchase #6 $158.64   5.349%   $167.1257   $167.13   $167.15   $167.10  
  Purchase #7 $118.95   13.335%   $134.812   $134.81   $134.80   $134.80  
  7 purchase totals = $900.01       $974.4506   $974.45   $974.40   $974.40