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 $69.28   13.503%   $78.6349   $78.63   $78.65   $78.60  
  Purchase #2 $153.91   5.237%   $161.9703   $161.97   $161.95   $162.00  
  Purchase #3 $144.68   3.197%   $149.3054   $149.31   $149.30   $149.30  
  Purchase #4 $99.39   7.676%   $107.0192   $107.02   $107.00   $107.00  
  Purchase #5 $250.89   13.685%   $285.2243   $285.22   $285.20   $285.20  
  Purchase #6 $122.60   12.660%   $138.1212   $138.12   $138.10   $138.10  
  Purchase #7 $142.98   7.686%   $153.9694   $153.97   $153.95   $154.00  
  7 purchase totals = $983.73       $1,074.2447   $1,074.24   $1,074.15   $1,074.20