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 $183.29   10.149%   $201.8921   $201.89   $201.90   $201.90  
  Purchase #2 $246.36   8.425%   $267.1158   $267.12   $267.10   $267.10  
  Purchase #3 $66.96   13.851%   $76.2346   $76.23   $76.25   $76.20  
  Purchase #4 $178.81   9.536%   $195.8613   $195.86   $195.85   $195.90  
  Purchase #5 $183.36   5.131%   $192.7682   $192.77   $192.75   $192.80  
  Purchase #6 $61.44   12.423%   $69.0727   $69.07   $69.05   $69.10  
  Purchase #7 $232.72   3.385%   $240.5976   $240.60   $240.60   $240.60  
  7 purchase totals = $1,152.94       $1,243.5423   $1,243.54   $1,243.50   $1,243.60