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 $56.82   7.369%   $61.0071   $61.01   $61.00   $61.00  
  Purchase #2 $89.85   9.337%   $98.2393   $98.24   $98.25   $98.20  
  Purchase #3 $250.88   7.178%   $268.8882   $268.89   $268.90   $268.90  
  Purchase #4 $242.63   4.483%   $253.5071   $253.51   $253.50   $253.50  
  Purchase #5 $67.41   4.659%   $70.5506   $70.55   $70.55   $70.60  
  Purchase #6 $67.82   9.145%   $74.0221   $74.02   $74.00   $74.00  
  Purchase #7 $24.91   7.461%   $26.7685   $26.77   $26.75   $26.80  
  7 purchase totals = $800.32       $852.9829   $852.99   $852.95   $853.00