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 $118.69   6.566%   $126.4832   $126.48   $126.50   $126.50  
  Purchase #2 $98.82   6.308%   $105.0536   $105.05   $105.05   $105.10  
  Purchase #3 $63.82   6.597%   $68.0302   $68.03   $68.05   $68.00  
  Purchase #4 $90.73   7.231%   $97.2907   $97.29   $97.30   $97.30  
  Purchase #5 $109.36   9.382%   $119.6202   $119.62   $119.60   $119.60  
  Purchase #6 $240.45   3.704%   $249.3563   $249.36   $249.35   $249.40  
  Purchase #7 $216.37   12.143%   $242.6438   $242.64   $242.65   $242.60  
  7 purchase totals = $938.24       $1,008.4780   $1,008.47   $1,008.50   $1,008.50