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 $104.97   13.325%   $118.9573   $118.96   $118.95   $119.00  
  Purchase #2 $214.32   8.452%   $232.4343   $232.43   $232.45   $232.40  
  Purchase #3 $229.32   8.151%   $248.0119   $248.01   $248.00   $248.00  
  Purchase #4 $217.99   11.142%   $242.2784   $242.28   $242.30   $242.30  
  Purchase #5 $234.89   10.867%   $260.4155   $260.42   $260.40   $260.40  
  Purchase #6 $37.76   7.223%   $40.4874   $40.49   $40.50   $40.50  
  Purchase #7 $160.36   9.554%   $175.6808   $175.68   $175.70   $175.70  
  7 purchase totals = $1,199.61       $1,318.2656   $1,318.27   $1,318.30   $1,318.30