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	$173.66	9.727%	$190.5519	$190.55	$190.55	$190.60
Purchase #2	$52.84	6.685%	$56.3724	$56.37	$56.35	$56.40
Purchase #3	$204.66	8.364%	$221.7778	$221.78	$221.80	$221.80
Purchase #4	$104.89	6.667%	$111.883	$111.88	$111.90	$111.90
Purchase #5	$91.84	13.845%	$104.5552	$104.56	$104.55	$104.60
Purchase #6	$122.72	7.209%	$131.5669	$131.57	$131.55	$131.60
Purchase #7	$236.82	5.566%	$250.0014	$250.00	$250.00	$250.00
7 purchase totals =	$987.43		$1,066.7086	$1,066.71	$1,066.70	$1,066.90