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 $180.45   8.596%   $195.9615   $195.96   $195.95   $196.00  
  Purchase #2 $196.61   10.434%   $217.1243   $217.12   $217.10   $217.10  
  Purchase #3 $139.49   7.346%   $149.7369   $149.74   $149.75   $149.70  
  Purchase #4 $54.65   7.378%   $58.6821   $58.68   $58.70   $58.70  
  Purchase #5 $54.98   9.689%   $60.307   $60.31   $60.30   $60.30  
  Purchase #6 $131.77   6.854%   $140.8015   $140.80   $140.80   $140.80  
  Purchase #7 $29.34   13.871%   $33.4098   $33.41   $33.40   $33.40  
  7 purchase totals = $787.29       $856.0231   $856.02   $856.00   $856.00