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 $245.53   7.563%   $264.0994   $264.10   $264.10   $264.10  
  Purchase #2 $14.56   8.501%   $15.7977   $15.80   $15.80   $15.80  
  Purchase #3 $60.89   5.719%   $64.3723   $64.37   $64.35   $64.40  
  Purchase #4 $69.47   3.534%   $71.9251   $71.93   $71.95   $71.90  
  Purchase #5 $186.79   12.771%   $210.645   $210.65   $210.65   $210.60  
  Purchase #6 $220.86   5.828%   $233.7317   $233.73   $233.75   $233.70  
  Purchase #7 $200.38   3.476%   $207.3452   $207.35   $207.35   $207.30  
  7 purchase totals = $998.48       $1,067.9164   $1,067.93   $1,067.95   $1,067.80