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 $197.53   11.538%   $220.321   $220.32   $220.30   $220.30  
  Purchase #2 $168.87   4.794%   $176.9656   $176.97   $176.95   $177.00  
  Purchase #3 $67.98   4.203%   $70.8372   $70.84   $70.85   $70.80  
  Purchase #4 $231.92   5.324%   $244.2674   $244.27   $244.25   $244.30  
  Purchase #5 $97.37   8.479%   $105.626   $105.63   $105.65   $105.60  
  Purchase #6 $151.25   9.771%   $166.0286   $166.03   $166.05   $166.00  
  Purchase #7 $40.67   13.748%   $46.2613   $46.26   $46.25   $46.30  
  7 purchase totals = $955.59       $1,030.3071   $1,030.32   $1,030.30   $1,030.30