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 $226.68   10.179%   $249.7538   $249.75   $249.75   $249.80  
  Purchase #2 $6.39   13.491%   $7.2521   $7.25   $7.25   $7.30  
  Purchase #3 $161.79   3.243%   $167.0368   $167.04   $167.05   $167.00  
  Purchase #4 $139.55   9.464%   $152.757   $152.76   $152.75   $152.80  
  Purchase #5 $107.39   3.599%   $111.255   $111.26   $111.25   $111.30  
  Purchase #6 $222.97   8.176%   $241.2   $241.20   $241.20   $241.20  
  Purchase #7 $14.69   11.136%   $16.3259   $16.33   $16.35   $16.30  
  7 purchase totals = $879.46       $945.5806   $945.59   $945.60   $945.70