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 $112.86   11.217%   $125.5195   $125.52   $125.50   $125.50  
  Purchase #2 $27.67   8.847%   $30.118   $30.12   $30.10   $30.10  
  Purchase #3 $224.80   11.301%   $250.2046   $250.20   $250.20   $250.20  
  Purchase #4 $115.48   8.412%   $125.1942   $125.19   $125.20   $125.20  
  Purchase #5 $196.28   4.302%   $204.724   $204.72   $204.70   $204.70  
  Purchase #6 $13.82   8.274%   $14.9635   $14.96   $14.95   $15.00  
  Purchase #7 $171.73   12.607%   $193.38   $193.38   $193.40   $193.40  
  7 purchase totals = $862.64       $944.1038   $944.09   $944.05   $944.10