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 $168.96   9.658%   $185.2782   $185.28   $185.30   $185.30  
  Purchase #2 $119.71   11.418%   $133.3785   $133.38   $133.40   $133.40  
  Purchase #3 $26.76   9.260%   $29.238   $29.24   $29.25   $29.20  
  Purchase #4 $183.83   12.558%   $206.9154   $206.92   $206.90   $206.90  
  Purchase #5 $160.87   3.565%   $166.605   $166.61   $166.60   $166.60  
  Purchase #6 $112.33   10.467%   $124.0876   $124.09   $124.10   $124.10  
  Purchase #7 $100.79   9.325%   $110.1887   $110.19   $110.20   $110.20  
  7 purchase totals = $873.25       $955.6914   $955.71   $955.75   $955.70