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 $78.68   9.519%   $86.1695   $86.17   $86.15   $86.20  
  Purchase #2 $190.28   8.112%   $205.7155   $205.72   $205.70   $205.70  
  Purchase #3 $134.26   7.667%   $144.5537   $144.55   $144.55   $144.60  
  Purchase #4 $114.91   10.769%   $127.2847   $127.28   $127.30   $127.30  
  Purchase #5 $193.40   10.126%   $212.9837   $212.98   $213.00   $213.00  
  Purchase #6 $103.44   10.583%   $114.3871   $114.39   $114.40   $114.40  
  Purchase #7 $180.68   11.258%   $201.021   $201.02   $201.00   $201.00  
  7 purchase totals = $995.65       $1,092.1152   $1,092.11   $1,092.10   $1,092.20