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 $60.79   9.598%   $66.6246   $66.62   $66.60   $66.60  
  Purchase #2 $83.88   3.309%   $86.6556   $86.66   $86.65   $86.70  
  Purchase #3 $40.25   10.504%   $44.4779   $44.48   $44.50   $44.50  
  Purchase #4 $61.54   8.165%   $66.5647   $66.56   $66.55   $66.60  
  Purchase #5 $216.66   13.232%   $245.3285   $245.33   $245.35   $245.30  
  Purchase #6 $64.66   5.860%   $68.4491   $68.45   $68.45   $68.40  
  Purchase #7 $156.56   8.282%   $169.5263   $169.53   $169.55   $169.50  
  7 purchase totals = $684.34       $747.6267   $747.63   $747.65   $747.60