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 $70.66   3.651%   $73.2398   $73.24   $73.25   $73.20  
  Purchase #2 $228.69   7.837%   $246.6124   $246.61   $246.60   $246.60  
  Purchase #3 $173.58   12.471%   $195.2272   $195.23   $195.25   $195.20  
  Purchase #4 $57.66   7.778%   $62.1448   $62.14   $62.15   $62.10  
  Purchase #5 $219.83   7.736%   $236.836   $236.84   $236.85   $236.80  
  Purchase #6 $34.35   4.233%   $35.804   $35.80   $35.80   $35.80  
  Purchase #7 $52.96   13.831%   $60.2849   $60.28   $60.30   $60.30  
  7 purchase totals = $837.73       $910.1491   $910.14   $910.20   $910.00