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 $239.86   11.584%   $267.6454   $267.65   $267.65   $267.60  
  Purchase #2 $92.28   4.196%   $96.1521   $96.15   $96.15   $96.20  
  Purchase #3 $218.81   4.141%   $227.8709   $227.87   $227.85   $227.90  
  Purchase #4 $190.49   12.646%   $214.5794   $214.58   $214.60   $214.60  
  Purchase #5 $57.50   9.319%   $62.8584   $62.86   $62.85   $62.90  
  Purchase #6 $65.82   7.481%   $70.744   $70.74   $70.75   $70.70  
  Purchase #7 $8.95   3.395%   $9.2539   $9.25   $9.25   $9.30  
  7 purchase totals = $873.71       $949.1041   $949.10   $949.10   $949.20