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 $51.82   13.567%   $58.8504   $58.85   $58.85   $58.90  
  Purchase #2 $58.98   3.597%   $61.1015   $61.10   $61.10   $61.10  
  Purchase #3 $244.92   9.452%   $268.0698   $268.07   $268.05   $268.10  
  Purchase #4 $208.29   13.732%   $236.8924   $236.89   $236.90   $236.90  
  Purchase #5 $13.65   12.404%   $15.3431   $15.34   $15.35   $15.30  
  Purchase #6 $210.38   6.220%   $223.4656   $223.47   $223.45   $223.50  
  Purchase #7 $47.77   7.497%   $51.3513   $51.35   $51.35   $51.40  
  7 purchase totals = $835.81       $915.0741   $915.07   $915.05   $915.20