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 $204.94   3.427%   $211.9633   $211.96   $211.95   $212.00  
  Purchase #2 $186.29   4.544%   $194.755   $194.76   $194.75   $194.80  
  Purchase #3 $30.28   13.256%   $34.2939   $34.29   $34.30   $34.30  
  Purchase #4 $73.92   3.313%   $76.369   $76.37   $76.35   $76.40  
  Purchase #5 $162.41   8.431%   $176.1028   $176.10   $176.10   $176.10  
  Purchase #6 $109.45   6.696%   $116.7788   $116.78   $116.80   $116.80  
  Purchase #7 $111.57   3.845%   $115.8599   $115.86   $115.85   $115.90  
  7 purchase totals = $878.86       $926.1227   $926.12   $926.10   $926.30