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 $35.67   8.249%   $38.6124   $38.61   $38.60   $38.60  
  Purchase #2 $224.44   10.779%   $248.6324   $248.63   $248.65   $248.60  
  Purchase #3 $184.42   4.642%   $192.9808   $192.98   $193.00   $193.00  
  Purchase #4 $132.95   11.734%   $148.5504   $148.55   $148.55   $148.60  
  Purchase #5 $71.87   6.550%   $76.5775   $76.58   $76.60   $76.60  
  Purchase #6 $115.91   7.257%   $124.3216   $124.32   $124.30   $124.30  
  Purchase #7 $109.87   8.367%   $119.0628   $119.06   $119.05   $119.10  
  7 purchase totals = $875.13       $948.7379   $948.73   $948.75   $948.80