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 $194.41   3.137%   $200.5086   $200.51   $200.50   $200.50  
  Purchase #2 $32.78   6.655%   $34.9615   $34.96   $34.95   $35.00  
  Purchase #3 $65.78   8.731%   $71.5233   $71.52   $71.50   $71.50  
  Purchase #4 $185.97   10.331%   $205.1826   $205.18   $205.20   $205.20  
  Purchase #5 $221.41   12.551%   $249.1992   $249.20   $249.20   $249.20  
  Purchase #6 $112.39   11.638%   $125.4699   $125.47   $125.45   $125.50  
  Purchase #7 $61.88   7.277%   $66.383   $66.38   $66.40   $66.40  
  7 purchase totals = $874.62       $953.2281   $953.22   $953.20   $953.30