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 $237.49   11.269%   $264.2527   $264.25   $264.25   $264.30  
  Purchase #2 $245.76   11.297%   $273.5235   $273.52   $273.50   $273.50  
  Purchase #3 $35.75   9.403%   $39.1116   $39.11   $39.10   $39.10  
  Purchase #4 $70.62   8.800%   $76.8346   $76.83   $76.85   $76.80  
  Purchase #5 $70.46   4.737%   $73.7977   $73.80   $73.80   $73.80  
  Purchase #6 $165.85   7.634%   $178.511   $178.51   $178.50   $178.50  
  Purchase #7 $33.79   7.202%   $36.2236   $36.22   $36.20   $36.20  
  7 purchase totals = $859.72       $942.2547   $942.24   $942.20   $942.20