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 $23.49   11.684%   $26.2346   $26.23   $26.25   $26.20  
  Purchase #2 $95.40   13.851%   $108.6139   $108.61   $108.60   $108.60  
  Purchase #3 $145.44   3.475%   $150.494   $150.49   $150.50   $150.50  
  Purchase #4 $149.53   8.796%   $162.6827   $162.68   $162.70   $162.70  
  Purchase #5 $92.30   3.193%   $95.2471   $95.25   $95.25   $95.20  
  Purchase #6 $171.42   13.761%   $195.0091   $195.01   $195.00   $195.00  
  Purchase #7 $180.38   12.332%   $202.6245   $202.62   $202.60   $202.60  
  7 purchase totals = $857.96       $940.9059   $940.89   $940.90   $940.80