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 $159.86   7.619%   $172.0397   $172.04   $172.05   $172.00  
  Purchase #2 $238.44   5.295%   $251.0654   $251.07   $251.05   $251.10  
  Purchase #3 $62.39   9.429%   $68.2728   $68.27   $68.25   $68.30  
  Purchase #4 $77.71   10.722%   $86.0421   $86.04   $86.05   $86.00  
  Purchase #5 $184.87   12.871%   $208.6646   $208.66   $208.65   $208.70  
  Purchase #6 $88.87   13.279%   $100.671   $100.67   $100.65   $100.70  
  Purchase #7 $129.83   5.198%   $136.5786   $136.58   $136.60   $136.60  
  7 purchase totals = $941.97       $1,023.3342   $1,023.33   $1,023.30   $1,023.40