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 $89.26   7.851%   $96.2678   $96.27   $96.25   $96.30  
  Purchase #2 $52.32   7.667%   $56.3314   $56.33   $56.35   $56.30  
  Purchase #3 $82.43   4.854%   $86.4312   $86.43   $86.45   $86.40  
  Purchase #4 $156.92   8.730%   $170.6191   $170.62   $170.60   $170.60  
  Purchase #5 $129.54   9.809%   $142.2466   $142.25   $142.25   $142.20  
  Purchase #6 $154.84   8.564%   $168.1005   $168.10   $168.10   $168.10  
  Purchase #7 $153.63   13.284%   $174.0382   $174.04   $174.05   $174.00  
  7 purchase totals = $818.94       $894.0348   $894.04   $894.05   $893.90