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	$19.55	6.631%	$20.8464	$20.85	$20.85	$20.80
Purchase #2	$133.98	9.447%	$146.6371	$146.64	$146.65	$146.60
Purchase #3	$151.63	11.124%	$168.4973	$168.50	$168.50	$168.50
Purchase #4	$178.69	7.268%	$191.6772	$191.68	$191.70	$191.70
Purchase #5	$66.89	9.271%	$73.0914	$73.09	$73.10	$73.10
Purchase #6	$193.56	3.332%	$200.0094	$200.01	$200.00	$200.00
Purchase #7	$196.88	11.532%	$219.5842	$219.58	$219.60	$219.60
7 purchase totals =	$941.18		$1,020.3430	$1,020.35	$1,020.40	$1,020.30