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 $14.45   10.303%   $15.9388   $15.94   $15.95   $15.90  
  Purchase #2 $29.30   9.598%   $32.1122   $32.11   $32.10   $32.10  
  Purchase #3 $34.61   12.362%   $38.8885   $38.89   $38.90   $38.90  
  Purchase #4 $149.91   3.377%   $154.9725   $154.97   $154.95   $155.00  
  Purchase #5 $117.92   3.427%   $121.9611   $121.96   $121.95   $122.00  
  Purchase #6 $8.26   9.780%   $9.0678   $9.07   $9.05   $9.10  
  Purchase #7 $187.26   7.128%   $200.6079   $200.61   $200.60   $200.60  
  7 purchase totals = $541.71       $573.5488   $573.55   $573.50   $573.60