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	$89.65	12.286%	$100.6644	$100.66	$100.65	$100.70
Purchase #2	$58.79	4.429%	$61.3938	$61.39	$61.40	$61.40
Purchase #3	$172.40	3.451%	$178.3495	$178.35	$178.35	$178.30
Purchase #4	$92.71	7.325%	$99.501	$99.50	$99.50	$99.50
Purchase #5	$102.88	12.133%	$115.3624	$115.36	$115.35	$115.40
Purchase #6	$30.54	8.278%	$33.0681	$33.07	$33.05	$33.10
Purchase #7	$142.79	11.364%	$159.0167	$159.02	$159.00	$159.00
7 purchase totals =	$689.76		$747.3559	$747.35	$747.30	$747.40