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 $204.53   6.196%   $217.2027   $217.20   $217.20   $217.20  
  Purchase #2 $82.95   3.688%   $86.0092   $86.01   $86.00   $86.00  
  Purchase #3 $117.62   13.749%   $133.7916   $133.79   $133.80   $133.80  
  Purchase #4 $215.78   13.723%   $245.3915   $245.39   $245.40   $245.40  
  Purchase #5 $23.45   5.769%   $24.8028   $24.80   $24.80   $24.80  
  Purchase #6 $170.60   8.699%   $185.4405   $185.44   $185.45   $185.40  
  Purchase #7 $140.97   11.196%   $156.753   $156.75   $156.75   $156.80  
  7 purchase totals = $955.90       $1,049.3913   $1,049.38   $1,049.40   $1,049.40