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 $183.90   12.687%   $207.2314   $207.23   $207.25   $207.20  
  Purchase #2 $157.49   8.624%   $171.0719   $171.07   $171.05   $171.10  
  Purchase #3 $94.34   4.151%   $98.2561   $98.26   $98.25   $98.30  
  Purchase #4 $242.95   7.347%   $260.7995   $260.80   $260.80   $260.80  
  Purchase #5 $29.27   10.267%   $32.2752   $32.28   $32.30   $32.30  
  Purchase #6 $151.99   4.493%   $158.8189   $158.82   $158.80   $158.80  
  Purchase #7 $72.79   6.594%   $77.5898   $77.59   $77.60   $77.60  
  7 purchase totals = $932.73       $1,006.0428   $1,006.05   $1,006.05   $1,006.10