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 $61.96   6.738%   $66.1349   $66.13   $66.15   $66.10  
  Purchase #2 $13.66   12.617%   $15.3835   $15.38   $15.40   $15.40  
  Purchase #3 $87.53   10.610%   $96.8169   $96.82   $96.80   $96.80  
  Purchase #4 $112.42   11.333%   $125.1606   $125.16   $125.15   $125.20  
  Purchase #5 $241.94   11.369%   $269.4462   $269.45   $269.45   $269.40  
  Purchase #6 $208.68   4.428%   $217.9204   $217.92   $217.90   $217.90  
  Purchase #7 $99.52   6.864%   $106.3511   $106.35   $106.35   $106.40  
  7 purchase totals = $825.71       $897.2136   $897.21   $897.20   $897.20