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	$206.38	13.195%	$233.6118	$233.61	$233.60	$233.60
Purchase #2	$247.46	13.360%	$280.5207	$280.52	$280.50	$280.50
Purchase #3	$113.94	11.700%	$127.271	$127.27	$127.25	$127.30
Purchase #4	$202.38	5.399%	$213.3065	$213.31	$213.30	$213.30
Purchase #5	$205.32	4.465%	$214.4875	$214.49	$214.50	$214.50
Purchase #6	$74.78	9.313%	$81.7443	$81.74	$81.75	$81.70
Purchase #7	$69.44	3.771%	$72.0586	$72.06	$72.05	$72.10
7 purchase totals =	$1,119.70		$1,223.0004	$1,223.00	$1,222.95	$1,223.00