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 $212.95   6.808%   $227.4476   $227.45   $227.45   $227.40  
  Purchase #2 $233.55   11.847%   $261.2187   $261.22   $261.20   $261.20  
  Purchase #3 $240.45   10.634%   $266.0195   $266.02   $266.00   $266.00  
  Purchase #4 $24.31   5.254%   $25.5872   $25.59   $25.60   $25.60  
  Purchase #5 $110.37   4.275%   $115.0883   $115.09   $115.10   $115.10  
  Purchase #6 $13.72   9.188%   $14.9806   $14.98   $15.00   $15.00  
  Purchase #7 $46.91   8.394%   $50.8476   $50.85   $50.85   $50.80  
  7 purchase totals = $882.26       $961.1895   $961.20   $961.20   $961.10