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 $44.45   9.499%   $48.6723   $48.67   $48.65   $48.70  
  Purchase #2 $62.73   6.768%   $66.9756   $66.98   $67.00   $67.00  
  Purchase #3 $134.26   8.345%   $145.464   $145.46   $145.45   $145.50  
  Purchase #4 $213.87   12.275%   $240.1225   $240.12   $240.10   $240.10  
  Purchase #5 $119.40   4.547%   $124.8291   $124.83   $124.85   $124.80  
  Purchase #6 $175.95   4.815%   $184.422   $184.42   $184.40   $184.40  
  Purchase #7 $124.35   7.111%   $133.1925   $133.19   $133.20   $133.20  
  7 purchase totals = $875.01       $943.6780   $943.67   $943.65   $943.70