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 $188.56   9.117%   $205.751   $205.75   $205.75   $205.80  
  Purchase #2 $217.60   3.864%   $226.0081   $226.01   $226.00   $226.00  
  Purchase #3 $23.62   10.109%   $26.0077   $26.01   $26.00   $26.00  
  Purchase #4 $52.41   5.583%   $55.3361   $55.34   $55.35   $55.30  
  Purchase #5 $92.92   9.628%   $101.8663   $101.87   $101.85   $101.90  
  Purchase #6 $169.51   4.749%   $177.56   $177.56   $177.55   $177.60  
  Purchase #7 $118.75   3.131%   $122.4681   $122.47   $122.45   $122.50  
  7 purchase totals = $863.37       $914.9973   $915.01   $914.95   $915.10