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 $230.68   9.628%   $252.8899   $252.89   $252.90   $252.90  
  Purchase #2 $83.51   13.301%   $94.6177   $94.62   $94.60   $94.60  
  Purchase #3 $203.54   8.221%   $220.273   $220.27   $220.25   $220.30  
  Purchase #4 $83.96   11.522%   $93.6339   $93.63   $93.65   $93.60  
  Purchase #5 $20.51   12.785%   $23.1322   $23.13   $23.15   $23.10  
  Purchase #6 $5.87   4.761%   $6.1495   $6.15   $6.15   $6.10  
  Purchase #7 $61.26   5.497%   $64.6275   $64.63   $64.65   $64.60  
  7 purchase totals = $689.33       $755.3237   $755.32   $755.35   $755.20