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 $50.97   10.510%   $56.3269   $56.33   $56.35   $56.30  
  Purchase #2 $41.62   12.314%   $46.7451   $46.75   $46.75   $46.70  
  Purchase #3 $95.76   13.186%   $108.3869   $108.39   $108.40   $108.40  
  Purchase #4 $50.32   6.561%   $53.6215   $53.62   $53.60   $53.60  
  Purchase #5 $147.90   3.603%   $153.2288   $153.23   $153.25   $153.20  
  Purchase #6 $218.28   9.559%   $239.1454   $239.15   $239.15   $239.10  
  Purchase #7 $190.33   8.345%   $206.213   $206.21   $206.20   $206.20  
  7 purchase totals = $795.18       $863.6676   $863.68   $863.70   $863.50