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 $192.51   11.774%   $215.1761   $215.18   $215.20   $215.20  
  Purchase #2 $200.66   13.392%   $227.5324   $227.53   $227.55   $227.50  
  Purchase #3 $108.91   9.173%   $118.9003   $118.90   $118.90   $118.90  
  Purchase #4 $22.51   9.402%   $24.6264   $24.63   $24.65   $24.60  
  Purchase #5 $139.77   8.796%   $152.0642   $152.06   $152.05   $152.10  
  Purchase #6 $76.47   11.120%   $84.9735   $84.97   $84.95   $85.00  
  Purchase #7 $48.90   8.424%   $53.0193   $53.02   $53.00   $53.00  
  7 purchase totals = $789.73       $876.2922   $876.29   $876.30   $876.30