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	$105.73	5.271%	$111.303	$111.30	$111.30	$111.30
Purchase #2	$191.60	4.804%	$200.8045	$200.80	$200.80	$200.80
Purchase #3	$180.63	7.523%	$194.2188	$194.22	$194.20	$194.20
Purchase #4	$180.86	10.352%	$199.5826	$199.58	$199.60	$199.60
Purchase #5	$18.95	9.472%	$20.7449	$20.74	$20.75	$20.70
Purchase #6	$31.78	12.147%	$35.6403	$35.64	$35.65	$35.60
Purchase #7	$82.67	7.410%	$88.7958	$88.80	$88.80	$88.80
7 purchase totals =	$792.22		$851.0899	$851.08	$851.10	$851.00