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	$154.84	3.227%	$159.8367	$159.84	$159.85	$159.80
Purchase #2	$134.56	10.291%	$148.4076	$148.41	$148.40	$148.40
Purchase #3	$166.54	12.539%	$187.4225	$187.42	$187.40	$187.40
Purchase #4	$118.80	3.631%	$123.1136	$123.11	$123.10	$123.10
Purchase #5	$13.89	11.379%	$15.4705	$15.47	$15.45	$15.50
Purchase #6	$185.42	3.258%	$191.461	$191.46	$191.45	$191.50
Purchase #7	$29.28	5.176%	$30.7955	$30.80	$30.80	$30.80
7 purchase totals =	$803.33		$856.5074	$856.51	$856.45	$856.50