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 $201.83   3.148%   $208.1836   $208.18   $208.20   $208.20  
  Purchase #2 $61.33   4.702%   $64.2137   $64.21   $64.20   $64.20  
  Purchase #3 $94.72   6.553%   $100.927   $100.93   $100.95   $100.90  
  Purchase #4 $215.36   5.563%   $227.3405   $227.34   $227.35   $227.30  
  Purchase #5 $109.64   4.128%   $114.1659   $114.17   $114.15   $114.20  
  Purchase #6 $140.56   12.732%   $158.4561   $158.46   $158.45   $158.50  
  Purchase #7 $72.38   6.375%   $76.9942   $76.99   $77.00   $77.00  
  7 purchase totals = $895.82       $950.2810   $950.28   $950.30   $950.30