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 $58.92   10.451%   $65.0777   $65.08   $65.10   $65.10  
  Purchase #2 $150.75   11.778%   $168.5053   $168.51   $168.50   $168.50  
  Purchase #3 $69.57   6.201%   $73.884   $73.88   $73.90   $73.90  
  Purchase #4 $239.47   3.607%   $248.1077   $248.11   $248.10   $248.10  
  Purchase #5 $14.70   3.811%   $15.2602   $15.26   $15.25   $15.30  
  Purchase #6 $146.75   9.165%   $160.1996   $160.20   $160.20   $160.20  
  Purchase #7 $184.78   12.582%   $208.029   $208.03   $208.05   $208.00  
  7 purchase totals = $864.94       $939.0635   $939.07   $939.10   $939.10