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 $13.82   6.601%   $14.7323   $14.73   $14.75   $14.70  
  Purchase #2 $235.57   11.786%   $263.3343   $263.33   $263.35   $263.30  
  Purchase #3 $155.98   5.723%   $164.9067   $164.91   $164.90   $164.90  
  Purchase #4 $9.63   12.726%   $10.8555   $10.86   $10.85   $10.90  
  Purchase #5 $84.47   9.244%   $92.2784   $92.28   $92.30   $92.30  
  Purchase #6 $8.72   10.111%   $9.6017   $9.60   $9.60   $9.60  
  Purchase #7 $67.32   13.241%   $76.2338   $76.23   $76.25   $76.20  
  7 purchase totals = $575.51       $631.9427   $631.94   $632.00   $631.90