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 $35.88   3.792%   $37.2406   $37.24   $37.25   $37.20  
  Purchase #2 $88.53   8.672%   $96.2073   $96.21   $96.20   $96.20  
  Purchase #3 $215.94   3.263%   $222.9861   $222.99   $223.00   $223.00  
  Purchase #4 $43.77   13.783%   $49.8028   $49.80   $49.80   $49.80  
  Purchase #5 $86.68   3.670%   $89.8612   $89.86   $89.85   $89.90  
  Purchase #6 $229.63   10.605%   $253.9823   $253.98   $254.00   $254.00  
  Purchase #7 $69.29   10.109%   $76.2945   $76.29   $76.30   $76.30  
  7 purchase totals = $769.72       $826.3748   $826.37   $826.40   $826.40