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 $217.90   10.770%   $241.3678   $241.37   $241.35   $241.40  
  Purchase #2 $232.60   11.846%   $260.1538   $260.15   $260.15   $260.20  
  Purchase #3 $96.26   11.439%   $107.2712   $107.27   $107.25   $107.30  
  Purchase #4 $24.98   13.258%   $28.2918   $28.29   $28.30   $28.30  
  Purchase #5 $69.55   6.689%   $74.2022   $74.20   $74.20   $74.20  
  Purchase #6 $15.25   4.566%   $15.9463   $15.95   $15.95   $15.90  
  Purchase #7 $231.60   11.731%   $258.769   $258.77   $258.75   $258.80  
  7 purchase totals = $888.14       $986.0021   $986.00   $985.95   $986.10