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 $49.91   11.451%   $55.6252   $55.63   $55.65   $55.60  
  Purchase #2 $68.29   5.701%   $72.1832   $72.18   $72.20   $72.20  
  Purchase #3 $90.82   7.832%   $97.933   $97.93   $97.95   $97.90  
  Purchase #4 $62.56   4.307%   $65.2545   $65.25   $65.25   $65.30  
  Purchase #5 $8.70   4.792%   $9.1169   $9.12   $9.10   $9.10  
  Purchase #6 $56.28   10.112%   $61.971   $61.97   $61.95   $62.00  
  Purchase #7 $247.98   7.451%   $266.457   $266.46   $266.45   $266.50  
  7 purchase totals = $584.54       $628.5408   $628.54   $628.55   $628.60