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 $112.43   12.598%   $126.5939   $126.59   $126.60   $126.60  
  Purchase #2 $95.91   8.493%   $104.0556   $104.06   $104.05   $104.10  
  Purchase #3 $193.33   12.531%   $217.5562   $217.56   $217.55   $217.60  
  Purchase #4 $247.38   12.825%   $279.1065   $279.11   $279.10   $279.10  
  Purchase #5 $23.65   5.801%   $25.0219   $25.02   $25.00   $25.00  
  Purchase #6 $48.54   11.572%   $54.157   $54.16   $54.15   $54.20  
  Purchase #7 $176.87   5.119%   $185.924   $185.92   $185.90   $185.90  
  7 purchase totals = $898.11       $992.4151   $992.42   $992.35   $992.50