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	$85.51	6.122%	$90.7449	$90.74	$90.75	$90.70
Purchase #2	$241.40	5.225%	$254.0132	$254.01	$254.00	$254.00
Purchase #3	$92.28	9.164%	$100.7365	$100.74	$100.75	$100.70
Purchase #4	$204.89	12.209%	$229.905	$229.91	$229.90	$229.90
Purchase #5	$231.83	7.382%	$248.9437	$248.94	$248.95	$248.90
Purchase #6	$98.45	6.323%	$104.675	$104.68	$104.70	$104.70
Purchase #7	$60.32	13.142%	$68.2473	$68.25	$68.25	$68.20
7 purchase totals =	$1,014.68		$1,097.2656	$1,097.27	$1,097.30	$1,097.10