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 $91.49   4.761%   $95.8458   $95.85   $95.85   $95.80  
  Purchase #2 $236.76   3.129%   $244.1682   $244.17   $244.15   $244.20  
  Purchase #3 $194.42   8.755%   $211.4415   $211.44   $211.45   $211.40  
  Purchase #4 $166.82   9.757%   $183.0966   $183.10   $183.10   $183.10  
  Purchase #5 $240.95   3.363%   $249.0531   $249.05   $249.05   $249.10  
  Purchase #6 $218.48   7.226%   $234.2674   $234.27   $234.25   $234.30  
  Purchase #7 $28.63   9.245%   $31.2768   $31.28   $31.30   $31.30  
  7 purchase totals = $1,177.55       $1,249.1494   $1,249.16   $1,249.15   $1,249.20