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 $43.45   11.691%   $48.5297   $48.53   $48.55   $48.50  
  Purchase #2 $230.61   8.568%   $250.3687   $250.37   $250.35   $250.40  
  Purchase #3 $242.60   7.820%   $261.5713   $261.57   $261.55   $261.60  
  Purchase #4 $225.40   8.543%   $244.6559   $244.66   $244.65   $244.70  
  Purchase #5 $86.33   12.381%   $97.0185   $97.02   $97.00   $97.00  
  Purchase #6 $76.39   9.806%   $83.8808   $83.88   $83.90   $83.90  
  Purchase #7 $9.60   12.614%   $10.8109   $10.81   $10.80   $10.80  
  7 purchase totals = $914.38       $996.8358   $996.84   $996.80   $996.90