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 $20.32   7.237%   $21.7906   $21.79   $21.80   $21.80  
  Purchase #2 $15.91   11.696%   $17.7708   $17.77   $17.75   $17.80  
  Purchase #3 $32.90   9.539%   $36.0383   $36.04   $36.05   $36.00  
  Purchase #4 $35.55   11.775%   $39.736   $39.74   $39.75   $39.70  
  Purchase #5 $15.31   3.160%   $15.7938   $15.79   $15.80   $15.80  
  Purchase #6 $82.37   5.559%   $86.9489   $86.95   $86.95   $86.90  
  Purchase #7 $180.61   9.649%   $198.0371   $198.04   $198.05   $198.00  
  7 purchase totals = $382.97       $416.1155   $416.12   $416.15   $416.00