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 $33.58   13.239%   $38.0257   $38.03   $38.05   $38.00  
  Purchase #2 $218.26   7.407%   $234.4265   $234.43   $234.45   $234.40  
  Purchase #3 $204.37   6.636%   $217.932   $217.93   $217.95   $217.90  
  Purchase #4 $107.31   9.850%   $117.88   $117.88   $117.90   $117.90  
  Purchase #5 $234.59   13.734%   $266.8086   $266.81   $266.80   $266.80  
  Purchase #6 $89.26   3.854%   $92.7001   $92.70   $92.70   $92.70  
  Purchase #7 $106.90   10.105%   $117.7022   $117.70   $117.70   $117.70  
  7 purchase totals = $994.27       $1,085.4751   $1,085.48   $1,085.55   $1,085.40