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 $86.70   8.268%   $93.8684   $93.87   $93.85   $93.90  
  Purchase #2 $97.67   8.521%   $105.9925   $105.99   $106.00   $106.00  
  Purchase #3 $247.28   4.845%   $259.2607   $259.26   $259.25   $259.30  
  Purchase #4 $124.30   4.498%   $129.891   $129.89   $129.90   $129.90  
  Purchase #5 $171.49   5.212%   $180.4281   $180.43   $180.45   $180.40  
  Purchase #6 $137.82   3.306%   $142.3763   $142.38   $142.40   $142.40  
  Purchase #7 $81.53   7.133%   $87.3455   $87.35   $87.35   $87.30  
  7 purchase totals = $946.79       $999.1625   $999.17   $999.20   $999.20