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 $29.96   4.635%   $31.3486   $31.35   $31.35   $31.30  
  Purchase #2 $86.72   4.505%   $90.6267   $90.63   $90.65   $90.60  
  Purchase #3 $109.81   11.150%   $122.0538   $122.05   $122.05   $122.10  
  Purchase #4 $21.81   6.339%   $23.1925   $23.19   $23.20   $23.20  
  Purchase #5 $44.40   5.544%   $46.8615   $46.86   $46.85   $46.90  
  Purchase #6 $62.64   10.549%   $69.2479   $69.25   $69.25   $69.20  
  Purchase #7 $196.74   4.645%   $205.8786   $205.88   $205.90   $205.90  
  7 purchase totals = $552.08       $589.2096   $589.21   $589.25   $589.20