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 $68.62   11.110%   $76.2437   $76.24   $76.25   $76.20  
  Purchase #2 $188.82   10.415%   $208.4856   $208.49   $208.50   $208.50  
  Purchase #3 $101.98   5.854%   $107.9499   $107.95   $107.95   $107.90  
  Purchase #4 $57.39   4.760%   $60.1218   $60.12   $60.10   $60.10  
  Purchase #5 $205.80   4.224%   $214.493   $214.49   $214.50   $214.50  
  Purchase #6 $109.85   7.340%   $117.913   $117.91   $117.90   $117.90  
  Purchase #7 $136.82   13.448%   $155.2196   $155.22   $155.20   $155.20  
  7 purchase totals = $869.28       $940.4266   $940.42   $940.40   $940.30