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	$74.86	3.429%	$77.4269	$77.43	$77.45	$77.40
Purchase #2	$102.58	7.852%	$110.6346	$110.63	$110.65	$110.60
Purchase #3	$32.57	5.197%	$34.2627	$34.26	$34.25	$34.30
Purchase #4	$232.72	13.194%	$263.4251	$263.43	$263.45	$263.40
Purchase #5	$109.98	12.490%	$123.7165	$123.72	$123.70	$123.70
Purchase #6	$150.93	7.756%	$162.6361	$162.64	$162.65	$162.60
Purchase #7	$99.45	3.728%	$103.1575	$103.16	$103.15	$103.20
7 purchase totals =	$803.09		$875.2594	$875.27	$875.30	$875.20