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 $52.98   4.323%   $55.2703   $55.27   $55.25   $55.30  
  Purchase #2 $166.41   7.199%   $178.3899   $178.39   $178.40   $178.40  
  Purchase #3 $70.81   7.603%   $76.1937   $76.19   $76.20   $76.20  
  Purchase #4 $245.38   5.508%   $258.8955   $258.90   $258.90   $258.90  
  Purchase #5 $210.53   12.269%   $236.3599   $236.36   $236.35   $236.40  
  Purchase #6 $125.76   11.413%   $140.113   $140.11   $140.10   $140.10  
  Purchase #7 $152.35   9.658%   $167.064   $167.06   $167.05   $167.10  
  7 purchase totals = $1,024.22       $1,112.2863   $1,112.28   $1,112.25   $1,112.40