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 $86.40   9.295%   $94.4309   $94.43   $94.45   $94.40  
  Purchase #2 $250.97   7.388%   $269.5117   $269.51   $269.50   $269.50  
  Purchase #3 $52.35   6.463%   $55.7334   $55.73   $55.75   $55.70  
  Purchase #4 $166.99   12.443%   $187.7686   $187.77   $187.75   $187.80  
  Purchase #5 $79.68   6.740%   $85.0504   $85.05   $85.05   $85.10  
  Purchase #6 $140.26   3.234%   $144.796   $144.80   $144.80   $144.80  
  Purchase #7 $26.63   12.358%   $29.9209   $29.92   $29.90   $29.90  
  7 purchase totals = $803.28       $867.2119   $867.21   $867.20   $867.20