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	$38.84	12.713%	$43.7777	$43.78	$43.80	$43.80
Purchase #2	$123.59	13.353%	$140.093	$140.09	$140.10	$140.10
Purchase #3	$210.87	5.448%	$222.3582	$222.36	$222.35	$222.40
Purchase #4	$75.65	10.309%	$83.4488	$83.45	$83.45	$83.40
Purchase #5	$180.88	12.409%	$203.3254	$203.33	$203.35	$203.30
Purchase #6	$78.29	11.681%	$87.4351	$87.44	$87.45	$87.40
Purchase #7	$214.92	9.813%	$236.0101	$236.01	$236.00	$236.00
7 purchase totals =	$923.04		$1,016.4483	$1,016.46	$1,016.50	$1,016.40