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	$79.99	4.519%	$83.6047	$83.60	$83.60	$83.60
Purchase #2	$74.46	10.333%	$82.154	$82.15	$82.15	$82.20
Purchase #3	$69.52	12.244%	$78.032	$78.03	$78.05	$78.00
Purchase #4	$113.29	6.280%	$120.4046	$120.40	$120.40	$120.40
Purchase #5	$175.46	12.217%	$196.8959	$196.90	$196.90	$196.90
Purchase #6	$171.63	11.378%	$191.1581	$191.16	$191.15	$191.20
Purchase #7	$118.63	7.326%	$127.3208	$127.32	$127.30	$127.30
7 purchase totals =	$802.98		$879.5701	$879.56	$879.55	$879.60