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 $205.47   5.497%   $216.7647   $216.76   $216.75   $216.80  
  Purchase #2 $201.48   8.571%   $218.7489   $218.75   $218.75   $218.70  
  Purchase #3 $85.57   11.504%   $95.414   $95.41   $95.40   $95.40  
  Purchase #4 $128.62   7.105%   $137.7585   $137.76   $137.75   $137.80  
  Purchase #5 $165.32   6.815%   $176.5866   $176.59   $176.60   $176.60  
  Purchase #6 $128.61   3.283%   $132.8323   $132.83   $132.85   $132.80  
  Purchase #7 $24.95   4.166%   $25.9894   $25.99   $26.00   $26.00  
  7 purchase totals = $940.02       $1,004.0944   $1,004.09   $1,004.10   $1,004.10