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 $208.38   13.501%   $236.5134   $236.51   $236.50   $236.50  
  Purchase #2 $86.98   10.271%   $95.9137   $95.91   $95.90   $95.90  
  Purchase #3 $230.66   7.588%   $248.1625   $248.16   $248.15   $248.20  
  Purchase #4 $96.49   9.204%   $105.3709   $105.37   $105.35   $105.40  
  Purchase #5 $36.72   12.500%   $41.31   $41.31   $41.30   $41.30  
  Purchase #6 $183.87   9.835%   $201.9536   $201.95   $201.95   $202.00  
  Purchase #7 $176.92   6.180%   $187.8537   $187.85   $187.85   $187.90  
  7 purchase totals = $1,020.02       $1,117.0778   $1,117.06   $1,117.00   $1,117.20