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 $13.29   12.147%   $14.9043   $14.90   $14.90   $14.90  
  Purchase #2 $207.99   11.183%   $231.2495   $231.25   $231.25   $231.20  
  Purchase #3 $171.81   9.203%   $187.6217   $187.62   $187.60   $187.60  
  Purchase #4 $94.95   6.612%   $101.2281   $101.23   $101.25   $101.20  
  Purchase #5 $98.74   4.476%   $103.1596   $103.16   $103.15   $103.20  
  Purchase #6 $175.71   11.436%   $195.8042   $195.80   $195.80   $195.80  
  Purchase #7 $56.90   9.175%   $62.1206   $62.12   $62.10   $62.10  
  7 purchase totals = $819.39       $896.0880   $896.08   $896.05   $896.00