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 $11.64   8.482%   $12.6273   $12.63   $12.65   $12.60  
  Purchase #2 $250.34   7.860%   $270.0167   $270.02   $270.00   $270.00  
  Purchase #3 $19.37   9.821%   $21.2723   $21.27   $21.25   $21.30  
  Purchase #4 $56.49   11.116%   $62.7694   $62.77   $62.75   $62.80  
  Purchase #5 $155.85   8.865%   $169.6661   $169.67   $169.65   $169.70  
  Purchase #6 $226.95   6.747%   $242.2623   $242.26   $242.25   $242.30  
  Purchase #7 $243.88   9.122%   $266.1267   $266.13   $266.15   $266.10  
  7 purchase totals = $964.52       $1,044.7408   $1,044.75   $1,044.70   $1,044.80