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 $93.94   8.154%   $101.5999   $101.60   $101.60   $101.60  
  Purchase #2 $43.69   13.830%   $49.7323   $49.73   $49.75   $49.70  
  Purchase #3 $68.82   11.394%   $76.6614   $76.66   $76.65   $76.70  
  Purchase #4 $48.98   8.534%   $53.16   $53.16   $53.15   $53.20  
  Purchase #5 $203.81   11.519%   $227.2869   $227.29   $227.30   $227.30  
  Purchase #6 $64.34   10.720%   $71.2372   $71.24   $71.25   $71.20  
  Purchase #7 $38.28   8.799%   $41.6483   $41.65   $41.65   $41.60  
  7 purchase totals = $561.86       $621.3260   $621.33   $621.35   $621.30