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 $29.66   11.295%   $33.0101   $33.01   $33.00   $33.00  
  Purchase #2 $249.61   10.744%   $276.4281   $276.43   $276.45   $276.40  
  Purchase #3 $57.68   8.312%   $62.4744   $62.47   $62.45   $62.50  
  Purchase #4 $141.49   10.762%   $156.7172   $156.72   $156.70   $156.70  
  Purchase #5 $108.77   5.758%   $115.033   $115.03   $115.05   $115.00  
  Purchase #6 $185.33   5.174%   $194.919   $194.92   $194.90   $194.90  
  Purchase #7 $136.48   12.741%   $153.8689   $153.87   $153.85   $153.90  
  7 purchase totals = $909.02       $992.4507   $992.45   $992.40   $992.40