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 $60.37   11.233%   $67.1514   $67.15   $67.15   $67.20  
  Purchase #2 $250.35   9.179%   $273.3296   $273.33   $273.35   $273.30  
  Purchase #3 $44.73   11.547%   $49.895   $49.90   $49.90   $49.90  
  Purchase #4 $229.41   3.149%   $236.6341   $236.63   $236.65   $236.60  
  Purchase #5 $227.94   3.166%   $235.1566   $235.16   $235.15   $235.20  
  Purchase #6 $176.81   7.161%   $189.4714   $189.47   $189.45   $189.50  
  Purchase #7 $15.90   5.297%   $16.7422   $16.74   $16.75   $16.70  
  7 purchase totals = $1,005.51       $1,068.3803   $1,068.38   $1,068.40   $1,068.40