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 $124.68   8.235%   $134.9474   $134.95   $134.95   $134.90  
  Purchase #2 $70.55   7.579%   $75.897   $75.90   $75.90   $75.90  
  Purchase #3 $120.80   3.866%   $125.4701   $125.47   $125.45   $125.50  
  Purchase #4 $18.85   5.826%   $19.9482   $19.95   $19.95   $19.90  
  Purchase #5 $207.30   3.243%   $214.0227   $214.02   $214.00   $214.00  
  Purchase #6 $20.38   5.248%   $21.4495   $21.45   $21.45   $21.40  
  Purchase #7 $177.42   9.556%   $194.3743   $194.37   $194.35   $194.40  
  7 purchase totals = $739.98       $786.1092   $786.11   $786.05   $786.00