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 $227.39   12.688%   $256.2412   $256.24   $256.25   $256.20  
  Purchase #2 $44.29   10.607%   $48.9878   $48.99   $49.00   $49.00  
  Purchase #3 $57.36   8.508%   $62.2402   $62.24   $62.25   $62.20  
  Purchase #4 $60.41   8.532%   $65.5642   $65.56   $65.55   $65.60  
  Purchase #5 $154.92   6.702%   $165.3027   $165.30   $165.30   $165.30  
  Purchase #6 $172.39   12.683%   $194.2542   $194.25   $194.25   $194.30  
  Purchase #7 $234.89   5.749%   $248.3938   $248.39   $248.40   $248.40  
  7 purchase totals = $951.65       $1,040.9841   $1,040.97   $1,041.00   $1,041.00