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 $86.59   6.725%   $92.4132   $92.41   $92.40   $92.40  
  Purchase #2 $29.33   8.702%   $31.8823   $31.88   $31.90   $31.90  
  Purchase #3 $103.55   7.297%   $111.106   $111.11   $111.10   $111.10  
  Purchase #4 $195.26   5.603%   $206.2004   $206.20   $206.20   $206.20  
  Purchase #5 $125.57   7.538%   $135.0355   $135.04   $135.05   $135.00  
  Purchase #6 $13.56   13.569%   $15.4   $15.40   $15.40   $15.40  
  Purchase #7 $110.93   3.371%   $114.6695   $114.67   $114.65   $114.70  
  7 purchase totals = $664.79       $706.7069   $706.71   $706.70   $706.70