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 $61.79   7.844%   $66.6368   $66.64   $66.65   $66.60  
  Purchase #2 $234.37   4.754%   $245.5119   $245.51   $245.50   $245.50  
  Purchase #3 $144.89   7.177%   $155.2888   $155.29   $155.30   $155.30  
  Purchase #4 $20.62   12.643%   $23.227   $23.23   $23.25   $23.20  
  Purchase #5 $121.80   6.220%   $129.376   $129.38   $129.40   $129.40  
  Purchase #6 $189.91   10.742%   $210.3101   $210.31   $210.30   $210.30  
  Purchase #7 $112.30   5.493%   $118.4686   $118.47   $118.45   $118.50  
  7 purchase totals = $885.68       $948.8192   $948.83   $948.85   $948.80