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 $65.87   4.287%   $68.6938   $68.69   $68.70   $68.70  
  Purchase #2 $28.74   13.416%   $32.5958   $32.60   $32.60   $32.60  
  Purchase #3 $143.65   12.161%   $161.1193   $161.12   $161.10   $161.10  
  Purchase #4 $199.82   7.694%   $215.1942   $215.19   $215.20   $215.20  
  Purchase #5 $66.73   12.861%   $75.3121   $75.31   $75.30   $75.30  
  Purchase #6 $163.90   10.401%   $180.9472   $180.95   $180.95   $180.90  
  Purchase #7 $189.65   10.452%   $209.4722   $209.47   $209.45   $209.50  
  7 purchase totals = $858.36       $943.3346   $943.33   $943.30   $943.30