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 $241.47   8.131%   $261.1039   $261.10   $261.10   $261.10  
  Purchase #2 $232.83   3.650%   $241.3283   $241.33   $241.35   $241.30  
  Purchase #3 $226.81   7.561%   $243.9591   $243.96   $243.95   $244.00  
  Purchase #4 $194.97   6.423%   $207.4929   $207.49   $207.50   $207.50  
  Purchase #5 $150.98   13.755%   $171.7473   $171.75   $171.75   $171.70  
  Purchase #6 $148.92   11.786%   $166.4717   $166.47   $166.45   $166.50  
  Purchase #7 $13.94   8.517%   $15.1273   $15.13   $15.15   $15.10  
  7 purchase totals = $1,209.92       $1,307.2305   $1,307.23   $1,307.25   $1,307.20