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 $208.99   3.843%   $217.0215   $217.02   $217.00   $217.00  
  Purchase #2 $15.97   6.108%   $16.9454   $16.95   $16.95   $16.90  
  Purchase #3 $239.29   13.698%   $272.0679   $272.07   $272.05   $272.10  
  Purchase #4 $200.53   13.456%   $227.5133   $227.51   $227.50   $227.50  
  Purchase #5 $99.51   5.712%   $105.194   $105.19   $105.20   $105.20  
  Purchase #6 $48.93   6.758%   $52.2367   $52.24   $52.25   $52.20  
  Purchase #7 $222.66   5.734%   $235.4273   $235.43   $235.45   $235.40  
  7 purchase totals = $1,035.88       $1,126.4061   $1,126.41   $1,126.40   $1,126.30