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 $107.61   6.601%   $114.7133   $114.71   $114.70   $114.70  
  Purchase #2 $182.97   4.473%   $191.1542   $191.15   $191.15   $191.20  
  Purchase #3 $59.87   10.547%   $66.1845   $66.18   $66.20   $66.20  
  Purchase #4 $249.36   11.256%   $277.428   $277.43   $277.45   $277.40  
  Purchase #5 $103.26   8.415%   $111.9493   $111.95   $111.95   $111.90  
  Purchase #6 $120.39   8.473%   $130.5906   $130.59   $130.60   $130.60  
  Purchase #7 $127.39   3.704%   $132.1085   $132.11   $132.10   $132.10  
  7 purchase totals = $950.85       $1,024.1284   $1,024.12   $1,024.15   $1,024.10