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	$79.32	5.171%	$83.4216	$83.42	$83.40	$83.40
Purchase #2	$123.29	10.720%	$136.5067	$136.51	$136.50	$136.50
Purchase #3	$28.52	12.728%	$32.15	$32.15	$32.15	$32.20
Purchase #4	$106.56	13.218%	$120.6451	$120.65	$120.65	$120.60
Purchase #5	$84.66	7.648%	$91.1348	$91.13	$91.15	$91.10
Purchase #6	$109.75	12.490%	$123.4578	$123.46	$123.45	$123.50
Purchase #7	$230.35	8.419%	$249.7432	$249.74	$249.75	$249.70
7 purchase totals =	$762.45		$837.0592	$837.06	$837.05	$837.00