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 $46.89   6.535%   $49.9543   $49.95   $49.95   $50.00  
  Purchase #2 $200.97   6.311%   $213.6532   $213.65   $213.65   $213.70  
  Purchase #3 $105.69   4.246%   $110.1776   $110.18   $110.20   $110.20  
  Purchase #4 $13.26   10.431%   $14.6432   $14.64   $14.65   $14.60  
  Purchase #5 $25.65   7.198%   $27.4963   $27.50   $27.50   $27.50  
  Purchase #6 $57.61   9.280%   $62.9562   $62.96   $62.95   $63.00  
  Purchase #7 $210.87   6.312%   $224.1801   $224.18   $224.20   $224.20  
  7 purchase totals = $660.94       $703.0609   $703.06   $703.10   $703.20