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	$213.89	13.521%	$242.8101	$242.81	$242.80	$242.80
Purchase #2	$40.93	13.203%	$46.334	$46.33	$46.35	$46.30
Purchase #3	$214.70	7.346%	$230.4719	$230.47	$230.45	$230.50
Purchase #4	$43.94	3.501%	$45.4783	$45.48	$45.50	$45.50
Purchase #5	$39.55	9.425%	$43.2776	$43.28	$43.30	$43.30
Purchase #6	$170.84	9.396%	$186.8921	$186.89	$186.90	$186.90
Purchase #7	$172.77	8.804%	$187.9807	$187.98	$188.00	$188.00
7 purchase totals =	$896.62		$983.2447	$983.24	$983.30	$983.30