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 $62.53   9.174%   $68.2665   $68.27   $68.25   $68.30  
  Purchase #2 $231.88   10.578%   $256.4083   $256.41   $256.40   $256.40  
  Purchase #3 $23.41   12.150%   $26.2543   $26.25   $26.25   $26.30  
  Purchase #4 $71.46   9.115%   $77.9736   $77.97   $77.95   $78.00  
  Purchase #5 $54.64   4.735%   $57.2272   $57.23   $57.25   $57.20  
  Purchase #6 $141.26   6.631%   $150.627   $150.63   $150.65   $150.60  
  Purchase #7 $111.77   6.496%   $119.0306   $119.03   $119.05   $119.00  
  7 purchase totals = $696.95       $755.7875   $755.79   $755.80   $755.80