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 $95.61   12.280%   $107.3509   $107.35   $107.35   $107.40  
  Purchase #2 $239.47   5.135%   $251.7668   $251.77   $251.75   $251.80  
  Purchase #3 $123.29   10.485%   $136.217   $136.22   $136.20   $136.20  
  Purchase #4 $22.64   4.376%   $23.6307   $23.63   $23.65   $23.60  
  Purchase #5 $155.58   13.247%   $176.1897   $176.19   $176.20   $176.20  
  Purchase #6 $221.62   6.498%   $236.0209   $236.02   $236.00   $236.00  
  Purchase #7 $98.85   4.200%   $103.0017   $103.00   $103.00   $103.00  
  7 purchase totals = $957.06       $1,034.1777   $1,034.18   $1,034.15   $1,034.20