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 $200.44   4.276%   $209.0108   $209.01   $209.00   $209.00  
  Purchase #2 $20.95   9.194%   $22.8761   $22.88   $22.90   $22.90  
  Purchase #3 $60.63   9.817%   $66.582   $66.58   $66.60   $66.60  
  Purchase #4 $173.62   5.268%   $182.7663   $182.77   $182.75   $182.80  
  Purchase #5 $122.27   6.504%   $130.2224   $130.22   $130.20   $130.20  
  Purchase #6 $199.40   7.129%   $213.6152   $213.62   $213.60   $213.60  
  Purchase #7 $165.70   8.327%   $179.4978   $179.50   $179.50   $179.50  
  7 purchase totals = $943.01       $1,004.5706   $1,004.58   $1,004.55   $1,004.60