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 $221.97   9.114%   $242.2003   $242.20   $242.20   $242.20  
  Purchase #2 $203.45   7.367%   $218.4382   $218.44   $218.45   $218.40  
  Purchase #3 $199.68   8.618%   $216.8884   $216.89   $216.90   $216.90  
  Purchase #4 $60.57   5.212%   $63.7269   $63.73   $63.75   $63.70  
  Purchase #5 $122.44   4.465%   $127.9069   $127.91   $127.90   $127.90  
  Purchase #6 $212.60   3.151%   $219.299   $219.30   $219.30   $219.30  
  Purchase #7 $234.62   6.797%   $250.5671   $250.57   $250.55   $250.60  
  7 purchase totals = $1,255.33       $1,339.0268   $1,339.04   $1,339.05   $1,339.00