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 $231.83   13.551%   $263.2453   $263.25   $263.25   $263.20  
  Purchase #2 $103.45   5.293%   $108.9256   $108.93   $108.95   $108.90  
  Purchase #3 $73.93   3.196%   $76.2928   $76.29   $76.30   $76.30  
  Purchase #4 $21.74   10.273%   $23.9734   $23.97   $23.95   $24.00  
  Purchase #5 $219.34   6.824%   $234.3078   $234.31   $234.30   $234.30  
  Purchase #6 $170.45   10.474%   $188.3029   $188.30   $188.30   $188.30  
  Purchase #7 $143.79   12.308%   $161.4877   $161.49   $161.50   $161.50  
  7 purchase totals = $964.53       $1,056.5355   $1,056.54   $1,056.55   $1,056.50