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	$28.36	4.304%	$29.5806	$29.58	$29.60	$29.60
Purchase #2	$179.50	6.188%	$190.6075	$190.61	$190.60	$190.60
Purchase #3	$40.66	13.750%	$46.2508	$46.25	$46.25	$46.30
Purchase #4	$39.35	9.548%	$43.1071	$43.11	$43.10	$43.10
Purchase #5	$127.28	4.820%	$133.4149	$133.41	$133.40	$133.40
Purchase #6	$56.33	9.475%	$61.6673	$61.67	$61.65	$61.70
Purchase #7	$58.25	7.779%	$62.7813	$62.78	$62.80	$62.80
7 purchase totals =	$529.73		$567.4095	$567.41	$567.40	$567.50