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 $84.78   11.119%   $94.2067   $94.21   $94.20   $94.20  
  Purchase #2 $241.31   4.151%   $251.3268   $251.33   $251.35   $251.30  
  Purchase #3 $74.39   5.138%   $78.2122   $78.21   $78.20   $78.20  
  Purchase #4 $244.68   8.325%   $265.0496   $265.05   $265.05   $265.00  
  Purchase #5 $161.68   11.484%   $180.2473   $180.25   $180.25   $180.20  
  Purchase #6 $216.37   11.683%   $241.6485   $241.65   $241.65   $241.60  
  Purchase #7 $199.82   3.622%   $207.0575   $207.06   $207.05   $207.10  
  7 purchase totals = $1,223.03       $1,317.7486   $1,317.76   $1,317.75   $1,317.60