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 $33.63   8.196%   $36.3863   $36.39   $36.40   $36.40  
  Purchase #2 $228.47   5.774%   $241.6619   $241.66   $241.65   $241.70  
  Purchase #3 $220.98   11.523%   $246.4435   $246.44   $246.45   $246.40  
  Purchase #4 $59.94   5.471%   $63.2193   $63.22   $63.20   $63.20  
  Purchase #5 $86.37   4.117%   $89.9259   $89.93   $89.95   $89.90  
  Purchase #6 $233.94   8.335%   $253.4389   $253.44   $253.45   $253.40  
  Purchase #7 $10.92   11.795%   $12.208   $12.21   $12.20   $12.20  
  7 purchase totals = $874.25       $943.2838   $943.29   $943.30   $943.20