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 $59.39   12.650%   $66.9028   $66.90   $66.90   $66.90  
  Purchase #2 $239.62   12.120%   $268.6619   $268.66   $268.65   $268.70  
  Purchase #3 $244.71   3.616%   $253.5587   $253.56   $253.55   $253.60  
  Purchase #4 $209.96   3.379%   $217.0545   $217.05   $217.05   $217.10  
  Purchase #5 $108.79   4.216%   $113.3766   $113.38   $113.40   $113.40  
  Purchase #6 $214.68   13.310%   $243.2539   $243.25   $243.25   $243.30  
  Purchase #7 $122.33   12.633%   $137.7839   $137.78   $137.80   $137.80  
  7 purchase totals = $1,199.48       $1,300.5923   $1,300.58   $1,300.60   $1,300.80