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 $69.56   8.314%   $75.3432   $75.34   $75.35   $75.30  
  Purchase #2 $230.75   12.737%   $260.1406   $260.14   $260.15   $260.10  
  Purchase #3 $234.37   7.826%   $252.7118   $252.71   $252.70   $252.70  
  Purchase #4 $242.45   11.382%   $270.0457   $270.05   $270.05   $270.00  
  Purchase #5 $43.68   9.807%   $47.9637   $47.96   $47.95   $48.00  
  Purchase #6 $93.91   3.170%   $96.8869   $96.89   $96.90   $96.90  
  Purchase #7 $228.81   9.249%   $249.9726   $249.97   $249.95   $250.00  
  7 purchase totals = $1,143.53       $1,253.0645   $1,253.06   $1,253.05   $1,253.00