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	$238.51	6.418%	$253.8176	$253.82	$253.80	$253.80
Purchase #2	$44.59	13.274%	$50.5089	$50.51	$50.50	$50.50
Purchase #3	$97.68	6.159%	$103.6961	$103.70	$103.70	$103.70
Purchase #4	$18.77	7.600%	$20.1965	$20.20	$20.20	$20.20
Purchase #5	$93.60	7.415%	$100.5404	$100.54	$100.55	$100.50
Purchase #6	$106.40	7.794%	$114.6928	$114.69	$114.70	$114.70
Purchase #7	$247.32	12.763%	$278.8855	$278.89	$278.90	$278.90
7 purchase totals =	$846.87		$922.3378	$922.35	$922.35	$922.30