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 $23.80   11.524%   $26.5427   $26.54   $26.55   $26.50  
  Purchase #2 $88.72   8.479%   $96.2426   $96.24   $96.25   $96.20  
  Purchase #3 $204.71   8.312%   $221.7255   $221.73   $221.75   $221.70  
  Purchase #4 $119.54   4.428%   $124.8332   $124.83   $124.85   $124.80  
  Purchase #5 $193.41   4.794%   $202.6821   $202.68   $202.70   $202.70  
  Purchase #6 $117.76   12.334%   $132.2845   $132.28   $132.30   $132.30  
  Purchase #7 $57.76   6.767%   $61.6686   $61.67   $61.65   $61.70  
  7 purchase totals = $805.70       $865.9792   $865.97   $866.05   $865.90