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 $246.54   8.332%   $267.0817   $267.08   $267.10   $267.10  
  Purchase #2 $52.80   11.369%   $58.8028   $58.80   $58.80   $58.80  
  Purchase #3 $62.35   9.331%   $68.1679   $68.17   $68.15   $68.20  
  Purchase #4 $6.83   4.513%   $7.1382   $7.14   $7.15   $7.10  
  Purchase #5 $56.61   12.230%   $63.5334   $63.53   $63.55   $63.50  
  Purchase #6 $171.71   4.202%   $178.9253   $178.93   $178.95   $178.90  
  Purchase #7 $167.38   9.280%   $182.9129   $182.91   $182.90   $182.90  
  7 purchase totals = $764.22       $826.5622   $826.56   $826.60   $826.50