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 $58.77   7.669%   $63.2771   $63.28   $63.30   $63.30  
  Purchase #2 $44.84   6.763%   $47.8725   $47.87   $47.85   $47.90  
  Purchase #3 $81.78   3.497%   $84.6398   $84.64   $84.65   $84.60  
  Purchase #4 $242.42   4.870%   $254.2259   $254.23   $254.25   $254.20  
  Purchase #5 $197.51   6.603%   $210.5516   $210.55   $210.55   $210.60  
  Purchase #6 $156.94   3.111%   $161.8224   $161.82   $161.80   $161.80  
  Purchase #7 $76.98   12.297%   $86.4462   $86.45   $86.45   $86.40  
  7 purchase totals = $859.24       $908.8355   $908.84   $908.85   $908.80