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	$146.74	12.717%	$165.4009	$165.40	$165.40	$165.40
Purchase #2	$162.94	9.808%	$178.9212	$178.92	$178.90	$178.90
Purchase #3	$215.60	3.104%	$222.2922	$222.29	$222.30	$222.30
Purchase #4	$35.98	12.543%	$40.493	$40.49	$40.50	$40.50
Purchase #5	$198.81	4.529%	$207.8141	$207.81	$207.80	$207.80
Purchase #6	$144.66	12.309%	$162.4662	$162.47	$162.45	$162.50
Purchase #7	$39.94	8.436%	$43.3093	$43.31	$43.30	$43.30
7 purchase totals =	$944.67		$1,020.6969	$1,020.69	$1,020.65	$1,020.70