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 $69.69   4.429%   $72.7766   $72.78   $72.80   $72.80  
  Purchase #2 $192.38   5.344%   $202.6608   $202.66   $202.65   $202.70  
  Purchase #3 $82.78   13.801%   $94.2045   $94.20   $94.20   $94.20  
  Purchase #4 $107.33   4.801%   $112.4829   $112.48   $112.50   $112.50  
  Purchase #5 $57.27   5.355%   $60.3368   $60.34   $60.35   $60.30  
  Purchase #6 $199.73   13.552%   $226.7974   $226.80   $226.80   $226.80  
  Purchase #7 $214.32   10.509%   $236.8429   $236.84   $236.85   $236.80  
  7 purchase totals = $923.50       $1,006.1019   $1,006.10   $1,006.15   $1,006.10