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 $95.79   9.181%   $104.5845   $104.58   $104.60   $104.60  
  Purchase #2 $176.34   13.113%   $199.4635   $199.46   $199.45   $199.50  
  Purchase #3 $21.68   13.538%   $24.615   $24.62   $24.60   $24.60  
  Purchase #4 $248.32   7.339%   $266.5442   $266.54   $266.55   $266.50  
  Purchase #5 $110.70   8.825%   $120.4693   $120.47   $120.45   $120.50  
  Purchase #6 $203.74   6.204%   $216.38   $216.38   $216.40   $216.40  
  Purchase #7 $137.58   12.182%   $154.34   $154.34   $154.35   $154.30  
  7 purchase totals = $994.15       $1,086.3965   $1,086.39   $1,086.40   $1,086.40