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 $82.43   3.873%   $85.6225   $85.62   $85.60   $85.60  
  Purchase #2 $8.70   13.415%   $9.8671   $9.87   $9.85   $9.90  
  Purchase #3 $200.33   7.281%   $214.916   $214.92   $214.90   $214.90  
  Purchase #4 $91.91   3.683%   $95.295   $95.30   $95.30   $95.30  
  Purchase #5 $206.45   7.851%   $222.6584   $222.66   $222.65   $222.70  
  Purchase #6 $110.81   4.510%   $115.8075   $115.81   $115.80   $115.80  
  Purchase #7 $212.75   13.844%   $242.2031   $242.20   $242.20   $242.20  
  7 purchase totals = $913.38       $986.3696   $986.38   $986.30   $986.40