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 $137.54   12.131%   $154.225   $154.23   $154.25   $154.20  
  Purchase #2 $175.26   11.781%   $195.9074   $195.91   $195.90   $195.90  
  Purchase #3 $117.93   13.683%   $134.0664   $134.07   $134.05   $134.10  
  Purchase #4 $207.83   4.291%   $216.748   $216.75   $216.75   $216.70  
  Purchase #5 $60.31   13.297%   $68.3294   $68.33   $68.35   $68.30  
  Purchase #6 $167.54   8.142%   $181.1811   $181.18   $181.20   $181.20  
  Purchase #7 $244.38   3.310%   $252.469   $252.47   $252.45   $252.50  
  7 purchase totals = $1,110.79       $1,202.9263   $1,202.94   $1,202.95   $1,202.90