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 $224.84   7.633%   $242.002   $242.00   $242.00   $242.00  
  Purchase #2 $13.39   11.395%   $14.9158   $14.92   $14.90   $14.90  
  Purchase #3 $167.36   11.459%   $186.5378   $186.54   $186.55   $186.50  
  Purchase #4 $127.69   5.149%   $134.2648   $134.26   $134.25   $134.30  
  Purchase #5 $63.64   4.758%   $66.668   $66.67   $66.65   $66.70  
  Purchase #6 $222.82   6.803%   $237.9784   $237.98   $238.00   $238.00  
  Purchase #7 $176.38   12.114%   $197.7467   $197.75   $197.75   $197.70  
  7 purchase totals = $996.12       $1,080.1135   $1,080.12   $1,080.10   $1,080.10