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 $59.38   11.488%   $66.2016   $66.20   $66.20   $66.20  
  Purchase #2 $196.82   9.187%   $214.9019   $214.90   $214.90   $214.90  
  Purchase #3 $155.58   7.423%   $167.1287   $167.13   $167.15   $167.10  
  Purchase #4 $9.27   5.399%   $9.7705   $9.77   $9.75   $9.80  
  Purchase #5 $39.61   5.460%   $41.7727   $41.77   $41.75   $41.80  
  Purchase #6 $245.65   5.812%   $259.9272   $259.93   $259.95   $259.90  
  Purchase #7 $32.34   3.648%   $33.5198   $33.52   $33.50   $33.50  
  7 purchase totals = $738.65       $793.2224   $793.22   $793.20   $793.20