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 $241.48   3.312%   $249.4778   $249.48   $249.50   $249.50  
  Purchase #2 $128.50   9.568%   $140.7949   $140.79   $140.80   $140.80  
  Purchase #3 $179.36   10.482%   $198.1605   $198.16   $198.15   $198.20  
  Purchase #4 $60.74   11.574%   $67.77   $67.77   $67.75   $67.80  
  Purchase #5 $218.54   7.798%   $235.5817   $235.58   $235.60   $235.60  
  Purchase #6 $242.41   3.827%   $251.687   $251.69   $251.70   $251.70  
  Purchase #7 $87.75   3.471%   $90.7958   $90.80   $90.80   $90.80  
  7 purchase totals = $1,158.78       $1,234.2677   $1,234.27   $1,234.30   $1,234.40