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 $18.40   7.386%   $19.759   $19.76   $19.75   $19.80  
  Purchase #2 $174.60   7.831%   $188.2729   $188.27   $188.25   $188.30  
  Purchase #3 $244.50   13.165%   $276.6884   $276.69   $276.70   $276.70  
  Purchase #4 $80.63   4.806%   $84.5051   $84.51   $84.50   $84.50  
  Purchase #5 $169.45   3.272%   $174.9944   $174.99   $175.00   $175.00  
  Purchase #6 $14.37   13.413%   $16.2974   $16.30   $16.30   $16.30  
  Purchase #7 $21.71   7.746%   $23.3917   $23.39   $23.40   $23.40  
  7 purchase totals = $723.66       $783.9089   $783.91   $783.90   $784.00