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 $221.59   6.341%   $235.641   $235.64   $235.65   $235.60  
  Purchase #2 $90.56   5.759%   $95.7754   $95.78   $95.80   $95.80  
  Purchase #3 $60.30   4.748%   $63.163   $63.16   $63.15   $63.20  
  Purchase #4 $27.25   8.763%   $29.6379   $29.64   $29.65   $29.60  
  Purchase #5 $242.84   5.781%   $256.8786   $256.88   $256.90   $256.90  
  Purchase #6 $148.78   3.377%   $153.8043   $153.80   $153.80   $153.80  
  Purchase #7 $132.71   3.657%   $137.5632   $137.56   $137.55   $137.60  
  7 purchase totals = $924.03       $972.4634   $972.46   $972.50   $972.50