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 $196.53   8.140%   $212.5275   $212.53   $212.55   $212.50  
  Purchase #2 $95.74   13.438%   $108.6055   $108.61   $108.60   $108.60  
  Purchase #3 $108.35   10.522%   $119.7506   $119.75   $119.75   $119.80  
  Purchase #4 $225.32   12.863%   $254.3029   $254.30   $254.30   $254.30  
  Purchase #5 $197.62   4.387%   $206.2896   $206.29   $206.30   $206.30  
  Purchase #6 $205.81   9.867%   $226.1173   $226.12   $226.10   $226.10  
  Purchase #7 $199.33   6.423%   $212.133   $212.13   $212.15   $212.10  
  7 purchase totals = $1,228.70       $1,339.7264   $1,339.73   $1,339.75   $1,339.70