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 $248.61   7.210%   $266.5348   $266.53   $266.55   $266.50  
  Purchase #2 $87.74   12.790%   $98.9619   $98.96   $98.95   $99.00  
  Purchase #3 $198.46   5.453%   $209.282   $209.28   $209.30   $209.30  
  Purchase #4 $41.25   12.771%   $46.518   $46.52   $46.50   $46.50  
  Purchase #5 $194.85   4.471%   $203.5617   $203.56   $203.55   $203.60  
  Purchase #6 $240.43   6.730%   $256.6109   $256.61   $256.60   $256.60  
  Purchase #7 $106.45   8.494%   $115.4919   $115.49   $115.50   $115.50  
  7 purchase totals = $1,117.79       $1,196.9612   $1,196.95   $1,196.95   $1,197.00