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 $223.33   10.391%   $246.5362   $246.54   $246.55   $246.50  
  Purchase #2 $23.71   12.287%   $26.6232   $26.62   $26.60   $26.60  
  Purchase #3 $10.80   6.238%   $11.4737   $11.47   $11.45   $11.50  
  Purchase #4 $90.64   10.592%   $100.2406   $100.24   $100.25   $100.20  
  Purchase #5 $126.60   13.455%   $143.634   $143.63   $143.65   $143.60  
  Purchase #6 $236.83   11.275%   $263.5326   $263.53   $263.55   $263.50  
  Purchase #7 $71.60   13.248%   $81.0856   $81.09   $81.10   $81.10  
  7 purchase totals = $783.51       $873.1259   $873.12   $873.15   $873.00