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 $115.62   5.730%   $122.245   $122.25   $122.25   $122.20  
  Purchase #2 $232.50   12.120%   $260.679   $260.68   $260.70   $260.70  
  Purchase #3 $135.49   12.219%   $152.0455   $152.05   $152.05   $152.00  
  Purchase #4 $121.66   4.725%   $127.4084   $127.41   $127.40   $127.40  
  Purchase #5 $206.69   6.129%   $219.358   $219.36   $219.35   $219.40  
  Purchase #6 $216.85   11.329%   $241.4169   $241.42   $241.40   $241.40  
  Purchase #7 $136.85   8.536%   $148.5315   $148.53   $148.55   $148.50  
  7 purchase totals = $1,165.66       $1,271.6843   $1,271.70   $1,271.70   $1,271.60