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 $57.27   5.152%   $60.2206   $60.22   $60.20   $60.20  
  Purchase #2 $240.41   6.345%   $255.664   $255.66   $255.65   $255.70  
  Purchase #3 $163.82   3.249%   $169.1425   $169.14   $169.15   $169.10  
  Purchase #4 $60.96   10.706%   $67.4864   $67.49   $67.50   $67.50  
  Purchase #5 $46.36   9.712%   $50.8625   $50.86   $50.85   $50.90  
  Purchase #6 $237.40   3.376%   $245.4146   $245.41   $245.40   $245.40  
  Purchase #7 $107.86   5.414%   $113.6995   $113.70   $113.70   $113.70  
  7 purchase totals = $914.08       $962.4901   $962.48   $962.45   $962.50