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 $61.42   10.732%   $68.0116   $68.01   $68.00   $68.00  
  Purchase #2 $46.72   11.158%   $51.933   $51.93   $51.95   $51.90  
  Purchase #3 $23.88   3.696%   $24.7626   $24.76   $24.75   $24.80  
  Purchase #4 $171.59   9.594%   $188.0523   $188.05   $188.05   $188.10  
  Purchase #5 $120.46   8.454%   $130.6437   $130.64   $130.65   $130.60  
  Purchase #6 $92.62   12.856%   $104.5272   $104.53   $104.55   $104.50  
  Purchase #7 $5.34   5.756%   $5.6474   $5.65   $5.65   $5.60  
  7 purchase totals = $522.03       $573.5778   $573.57   $573.60   $573.50