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 $84.92   12.335%   $95.3949   $95.39   $95.40   $95.40  
  Purchase #2 $126.69   11.652%   $141.4519   $141.45   $141.45   $141.50  
  Purchase #3 $231.30   9.305%   $252.8225   $252.82   $252.80   $252.80  
  Purchase #4 $63.92   4.602%   $66.8616   $66.86   $66.85   $66.90  
  Purchase #5 $175.54   9.739%   $192.6358   $192.64   $192.65   $192.60  
  Purchase #6 $95.68   3.644%   $99.1666   $99.17   $99.15   $99.20  
  Purchase #7 $140.39   8.874%   $152.8482   $152.85   $152.85   $152.80  
  7 purchase totals = $918.44       $1,001.1815   $1,001.18   $1,001.15   $1,001.20