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 $83.35   3.118%   $85.9489   $85.95   $85.95   $85.90  
  Purchase #2 $143.40   8.271%   $155.2606   $155.26   $155.25   $155.30  
  Purchase #3 $194.81   8.515%   $211.3981   $211.40   $211.40   $211.40  
  Purchase #4 $69.87   7.285%   $74.96   $74.96   $74.95   $75.00  
  Purchase #5 $86.43   6.512%   $92.0583   $92.06   $92.05   $92.10  
  Purchase #6 $184.48   4.146%   $192.1285   $192.13   $192.15   $192.10  
  Purchase #7 $39.98   10.580%   $44.2099   $44.21   $44.20   $44.20  
  7 purchase totals = $802.32       $855.9643   $855.97   $855.95   $856.00