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 $75.26   9.530%   $82.4323   $82.43   $82.45   $82.40  
  Purchase #2 $240.62   10.632%   $266.2027   $266.20   $266.20   $266.20  
  Purchase #3 $106.97   10.177%   $117.8563   $117.86   $117.85   $117.90  
  Purchase #4 $53.98   8.508%   $58.5726   $58.57   $58.55   $58.60  
  Purchase #5 $85.59   7.656%   $92.1428   $92.14   $92.15   $92.10  
  Purchase #6 $6.84   8.812%   $7.4427   $7.44   $7.45   $7.40  
  Purchase #7 $246.92   4.310%   $257.5623   $257.56   $257.55   $257.60  
  7 purchase totals = $816.18       $882.2117   $882.20   $882.20   $882.20