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 $168.39   9.548%   $184.4679   $184.47   $184.45   $184.50  
  Purchase #2 $221.58   6.675%   $236.3705   $236.37   $236.35   $236.40  
  Purchase #3 $21.32   8.320%   $23.0938   $23.09   $23.10   $23.10  
  Purchase #4 $229.76   3.842%   $238.5874   $238.59   $238.60   $238.60  
  Purchase #5 $212.31   4.587%   $222.0487   $222.05   $222.05   $222.00  
  Purchase #6 $107.30   9.871%   $117.8916   $117.89   $117.90   $117.90  
  Purchase #7 $174.59   7.778%   $188.1696   $188.17   $188.15   $188.20  
  7 purchase totals = $1,135.25       $1,210.6295   $1,210.63   $1,210.60   $1,210.70