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 $18.29   8.609%   $19.8646   $19.86   $19.85   $19.90  
  Purchase #2 $36.98   4.666%   $38.7055   $38.71   $38.70   $38.70  
  Purchase #3 $215.41   13.496%   $244.4817   $244.48   $244.50   $244.50  
  Purchase #4 $73.28   5.624%   $77.4013   $77.40   $77.40   $77.40  
  Purchase #5 $233.87   5.353%   $246.3891   $246.39   $246.40   $246.40  
  Purchase #6 $138.54   13.761%   $157.6045   $157.60   $157.60   $157.60  
  Purchase #7 $213.43   4.275%   $222.5541   $222.55   $222.55   $222.60  
  7 purchase totals = $929.80       $1,007.0008   $1,006.99   $1,007.00   $1,007.10