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 $61.82   8.228%   $66.9065   $66.91   $66.90   $66.90  
  Purchase #2 $239.76   8.827%   $260.9236   $260.92   $260.90   $260.90  
  Purchase #3 $5.26   11.742%   $5.8776   $5.88   $5.90   $5.90  
  Purchase #4 $218.30   4.859%   $228.9072   $228.91   $228.90   $228.90  
  Purchase #5 $103.49   11.468%   $115.3582   $115.36   $115.35   $115.40  
  Purchase #6 $71.96   13.420%   $81.617   $81.62   $81.60   $81.60  
  Purchase #7 $232.37   9.542%   $254.5427   $254.54   $254.55   $254.50  
  7 purchase totals = $932.96       $1,014.1328   $1,014.14   $1,014.10   $1,014.10