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	$215.58	13.236%	$244.1142	$244.11	$244.10	$244.10
Purchase #2	$16.89	9.194%	$18.4429	$18.44	$18.45	$18.40
Purchase #3	$19.79	5.836%	$20.9449	$20.94	$20.95	$20.90
Purchase #4	$223.96	4.305%	$233.6015	$233.60	$233.60	$233.60
Purchase #5	$164.31	6.765%	$175.4256	$175.43	$175.45	$175.40
Purchase #6	$100.41	9.464%	$109.9128	$109.91	$109.90	$109.90
Purchase #7	$31.90	6.773%	$34.0606	$34.06	$34.05	$34.10
7 purchase totals =	$772.84		$836.5025	$836.49	$836.50	$836.40