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 $168.65   6.582%   $179.7505   $179.75   $179.75   $179.80  
  Purchase #2 $94.41   6.662%   $100.6996   $100.70   $100.70   $100.70  
  Purchase #3 $164.54   7.125%   $176.2635   $176.26   $176.25   $176.30  
  Purchase #4 $118.28   5.579%   $124.8788   $124.88   $124.90   $124.90  
  Purchase #5 $236.31   7.713%   $254.5366   $254.54   $254.55   $254.50  
  Purchase #6 $79.51   5.568%   $83.9371   $83.94   $83.95   $83.90  
  Purchase #7 $21.37   10.161%   $23.5414   $23.54   $23.55   $23.50  
  7 purchase totals = $883.07       $943.6075   $943.61   $943.65   $943.60