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	$29.82	4.130%	$31.0516	$31.05	$31.05	$31.10
Purchase #2	$153.44	12.572%	$172.7305	$172.73	$172.75	$172.70
Purchase #3	$176.44	8.111%	$190.751	$190.75	$190.75	$190.80
Purchase #4	$115.63	6.731%	$123.4131	$123.41	$123.40	$123.40
Purchase #5	$94.52	11.213%	$105.1185	$105.12	$105.10	$105.10
Purchase #6	$63.94	13.658%	$72.6729	$72.67	$72.65	$72.70
Purchase #7	$133.27	7.590%	$143.3852	$143.39	$143.40	$143.40
7 purchase totals =	$767.06		$839.1228	$839.12	$839.10	$839.20