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 $65.53   11.756%   $73.2337   $73.23   $73.25   $73.20  
  Purchase #2 $65.75   8.649%   $71.4367   $71.44   $71.45   $71.40  
  Purchase #3 $157.91   13.590%   $179.37   $179.37   $179.35   $179.40  
  Purchase #4 $162.89   5.829%   $172.3849   $172.38   $172.40   $172.40  
  Purchase #5 $210.63   5.281%   $221.7534   $221.75   $221.75   $221.80  
  Purchase #6 $22.53   4.869%   $23.627   $23.63   $23.65   $23.60  
  Purchase #7 $44.85   4.755%   $46.9826   $46.98   $47.00   $47.00  
  7 purchase totals = $730.09       $788.7883   $788.78   $788.85   $788.80