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 $53.94   5.573%   $56.9461   $56.95   $56.95   $56.90  
  Purchase #2 $230.82   13.122%   $261.1082   $261.11   $261.10   $261.10  
  Purchase #3 $150.49   8.531%   $163.3283   $163.33   $163.35   $163.30  
  Purchase #4 $85.32   6.838%   $91.1542   $91.15   $91.15   $91.20  
  Purchase #5 $242.67   5.327%   $255.597   $255.60   $255.60   $255.60  
  Purchase #6 $191.64   10.570%   $211.8963   $211.90   $211.90   $211.90  
  Purchase #7 $221.91   3.707%   $230.1362   $230.14   $230.15   $230.10  
  7 purchase totals = $1,176.79       $1,270.1663   $1,270.18   $1,270.20   $1,270.10