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 $67.33   9.349%   $73.6247   $73.62   $73.60   $73.60  
  Purchase #2 $166.59   11.429%   $185.6296   $185.63   $185.65   $185.60  
  Purchase #3 $212.44   6.713%   $226.7011   $226.70   $226.70   $226.70  
  Purchase #4 $15.54   3.782%   $16.1277   $16.13   $16.15   $16.10  
  Purchase #5 $40.67   3.857%   $42.2386   $42.24   $42.25   $42.20  
  Purchase #6 $146.32   3.279%   $151.1178   $151.12   $151.10   $151.10  
  Purchase #7 $28.99   6.261%   $30.8051   $30.81   $30.80   $30.80  
  7 purchase totals = $677.88       $726.2446   $726.25   $726.25   $726.10