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 $179.48   13.723%   $204.11   $204.11   $204.10   $204.10  
  Purchase #2 $44.41   3.487%   $45.9586   $45.96   $45.95   $46.00  
  Purchase #3 $41.79   5.600%   $44.1302   $44.13   $44.15   $44.10  
  Purchase #4 $94.73   3.197%   $97.7585   $97.76   $97.75   $97.80  
  Purchase #5 $83.67   9.293%   $91.4455   $91.45   $91.45   $91.40  
  Purchase #6 $191.95   13.387%   $217.6463   $217.65   $217.65   $217.60  
  Purchase #7 $249.89   9.802%   $274.3842   $274.38   $274.40   $274.40  
  7 purchase totals = $885.92       $975.4333   $975.44   $975.45   $975.40