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	$90.50	10.600%	$100.093	$100.09	$100.10	$100.10
Purchase #2	$129.50	9.151%	$141.3505	$141.35	$141.35	$141.40
Purchase #3	$25.98	9.350%	$28.4091	$28.41	$28.40	$28.40
Purchase #4	$16.35	9.120%	$17.8411	$17.84	$17.85	$17.80
Purchase #5	$82.52	11.335%	$91.8736	$91.87	$91.85	$91.90
Purchase #6	$33.88	13.839%	$38.5687	$38.57	$38.55	$38.60
Purchase #7	$184.58	11.569%	$205.9341	$205.93	$205.95	$205.90
7 purchase totals =	$563.31		$624.0701	$624.06	$624.05	$624.10