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 $96.26   10.873%   $106.7263   $106.73   $106.75   $106.70  
  Purchase #2 $88.71   9.756%   $97.3645   $97.36   $97.35   $97.40  
  Purchase #3 $235.53   6.224%   $250.1894   $250.19   $250.20   $250.20  
  Purchase #4 $100.65   11.732%   $112.4583   $112.46   $112.45   $112.50  
  Purchase #5 $172.70   13.168%   $195.4411   $195.44   $195.45   $195.40  
  Purchase #6 $14.31   11.266%   $15.9222   $15.92   $15.90   $15.90  
  Purchase #7 $115.28   8.813%   $125.4396   $125.44   $125.45   $125.40  
  7 purchase totals = $823.44       $903.5414   $903.54   $903.55   $903.50