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 $86.76   9.801%   $95.2633   $95.26   $95.25   $95.30  
  Purchase #2 $29.27   11.474%   $32.6284   $32.63   $32.65   $32.60  
  Purchase #3 $111.42   13.126%   $126.045   $126.05   $126.05   $126.00  
  Purchase #4 $88.61   6.363%   $94.2483   $94.25   $94.25   $94.20  
  Purchase #5 $152.73   3.444%   $157.99   $157.99   $158.00   $158.00  
  Purchase #6 $159.52   8.576%   $173.2004   $173.20   $173.20   $173.20  
  Purchase #7 $5.70   8.782%   $6.2006   $6.20   $6.20   $6.20  
  7 purchase totals = $634.01       $685.5760   $685.58   $685.60   $685.50