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 $146.31   4.796%   $153.327   $153.33   $153.35   $153.30  
  Purchase #2 $102.75   8.272%   $111.2495   $111.25   $111.25   $111.20  
  Purchase #3 $227.94   3.842%   $236.6975   $236.70   $236.70   $236.70  
  Purchase #4 $92.36   4.391%   $96.4155   $96.42   $96.40   $96.40  
  Purchase #5 $15.47   4.403%   $16.1511   $16.15   $16.15   $16.20  
  Purchase #6 $152.51   13.673%   $173.3627   $173.36   $173.35   $173.40  
  Purchase #7 $136.26   7.745%   $146.8133   $146.81   $146.80   $146.80  
  7 purchase totals = $873.60       $934.0166   $934.02   $934.00   $934.00