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 $211.28   5.763%   $223.4561   $223.46   $223.45   $223.50  
  Purchase #2 $157.75   11.650%   $176.1279   $176.13   $176.15   $176.10  
  Purchase #3 $182.96   5.614%   $193.2314   $193.23   $193.25   $193.20  
  Purchase #4 $93.25   4.167%   $97.1357   $97.14   $97.15   $97.10  
  Purchase #5 $167.92   9.351%   $183.6222   $183.62   $183.60   $183.60  
  Purchase #6 $195.41   9.593%   $214.1557   $214.16   $214.15   $214.20  
  Purchase #7 $158.82   8.721%   $172.6707   $172.67   $172.65   $172.70  
  7 purchase totals = $1,167.39       $1,260.3997   $1,260.41   $1,260.40   $1,260.40