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 $68.48   8.323%   $74.1796   $74.18   $74.20   $74.20  
  Purchase #2 $126.70   4.726%   $132.6878   $132.69   $132.70   $132.70  
  Purchase #3 $107.58   5.582%   $113.5851   $113.59   $113.60   $113.60  
  Purchase #4 $117.39   6.644%   $125.1894   $125.19   $125.20   $125.20  
  Purchase #5 $95.75   12.372%   $107.5962   $107.60   $107.60   $107.60  
  Purchase #6 $151.45   8.463%   $164.2672   $164.27   $164.25   $164.30  
  Purchase #7 $219.99   11.475%   $245.2339   $245.23   $245.25   $245.20  
  7 purchase totals = $887.34       $962.7392   $962.75   $962.80   $962.80