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 $241.99   5.513%   $255.3309   $255.33   $255.35   $255.30  
  Purchase #2 $168.99   4.160%   $176.02   $176.02   $176.00   $176.00  
  Purchase #3 $129.58   8.305%   $140.3416   $140.34   $140.35   $140.30  
  Purchase #4 $21.86   13.636%   $24.8408   $24.84   $24.85   $24.80  
  Purchase #5 $41.67   6.671%   $44.4498   $44.45   $44.45   $44.40  
  Purchase #6 $47.76   9.383%   $52.2413   $52.24   $52.25   $52.20  
  Purchase #7 $47.76   11.266%   $53.1406   $53.14   $53.15   $53.10  
  7 purchase totals = $699.61       $746.3650   $746.36   $746.40   $746.10