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 $65.54   4.622%   $68.5693   $68.57   $68.55   $68.60  
  Purchase #2 $160.85   7.786%   $173.3738   $173.37   $173.35   $173.40  
  Purchase #3 $144.69   10.560%   $159.9693   $159.97   $159.95   $160.00  
  Purchase #4 $95.27   5.274%   $100.2945   $100.29   $100.30   $100.30  
  Purchase #5 $185.86   13.621%   $211.176   $211.18   $211.20   $211.20  
  Purchase #6 $167.34   11.534%   $186.641   $186.64   $186.65   $186.60  
  Purchase #7 $215.76   6.322%   $229.4003   $229.40   $229.40   $229.40  
  7 purchase totals = $1,035.31       $1,129.4242   $1,129.42   $1,129.40   $1,129.50