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	$124.94	12.651%	$140.7462	$140.75	$140.75	$140.70
Purchase #2	$49.98	8.477%	$54.2168	$54.22	$54.20	$54.20
Purchase #3	$183.50	6.845%	$196.0606	$196.06	$196.05	$196.10
Purchase #4	$111.55	5.713%	$117.9229	$117.92	$117.90	$117.90
Purchase #5	$17.62	3.809%	$18.2911	$18.29	$18.30	$18.30
Purchase #6	$20.56	10.492%	$22.7172	$22.72	$22.70	$22.70
Purchase #7	$226.27	7.341%	$242.8805	$242.88	$242.90	$242.90
7 purchase totals =	$734.42		$792.8353	$792.84	$792.80	$792.80