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 $173.35   11.267%   $192.8813   $192.88   $192.90   $192.90  
  Purchase #2 $67.59   4.232%   $70.4504   $70.45   $70.45   $70.50  
  Purchase #3 $26.47   7.115%   $28.3533   $28.35   $28.35   $28.40  
  Purchase #4 $164.94   5.863%   $174.6104   $174.61   $174.60   $174.60  
  Purchase #5 $180.97   8.213%   $195.8331   $195.83   $195.85   $195.80  
  Purchase #6 $249.68   12.826%   $281.704   $281.70   $281.70   $281.70  
  Purchase #7 $72.67   10.854%   $80.5576   $80.56   $80.55   $80.60  
  7 purchase totals = $935.67       $1,024.3901   $1,024.38   $1,024.40   $1,024.50