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 $74.60   12.811%   $84.157   $84.16   $84.15   $84.20  
  Purchase #2 $67.79   7.500%   $72.8743   $72.87   $72.85   $72.90  
  Purchase #3 $104.69   10.823%   $116.0206   $116.02   $116.00   $116.00  
  Purchase #4 $201.70   7.831%   $217.4951   $217.50   $217.50   $217.50  
  Purchase #5 $41.43   10.337%   $45.7126   $45.71   $45.70   $45.70  
  Purchase #6 $214.50   3.200%   $221.364   $221.36   $221.35   $221.40  
  Purchase #7 $176.47   4.438%   $184.3017   $184.30   $184.30   $184.30  
  7 purchase totals = $881.18       $941.9253   $941.92   $941.85   $942.00