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 $82.51   13.780%   $93.8799   $93.88   $93.90   $93.90  
  Purchase #2 $112.65   11.787%   $125.9281   $125.93   $125.95   $125.90  
  Purchase #3 $225.96   13.387%   $256.2093   $256.21   $256.20   $256.20  
  Purchase #4 $249.44   4.480%   $260.6149   $260.61   $260.60   $260.60  
  Purchase #5 $216.55   7.366%   $232.5011   $232.50   $232.50   $232.50  
  Purchase #6 $157.48   7.829%   $169.8091   $169.81   $169.80   $169.80  
  Purchase #7 $59.33   11.685%   $66.2627   $66.26   $66.25   $66.30  
  7 purchase totals = $1,103.92       $1,205.2051   $1,205.20   $1,205.20   $1,205.20