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 $244.93   10.216%   $269.952   $269.95   $269.95   $270.00  
  Purchase #2 $197.28   12.699%   $222.3326   $222.33   $222.35   $222.30  
  Purchase #3 $44.81   7.758%   $48.2864   $48.29   $48.30   $48.30  
  Purchase #4 $35.28   5.187%   $37.11   $37.11   $37.10   $37.10  
  Purchase #5 $94.40   9.516%   $103.3831   $103.38   $103.40   $103.40  
  Purchase #6 $193.88   8.168%   $209.7161   $209.72   $209.70   $209.70  
  Purchase #7 $102.26   3.450%   $105.788   $105.79   $105.80   $105.80  
  7 purchase totals = $912.84       $996.5682   $996.57   $996.60   $996.60