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	$16.65	12.492%	$18.7299	$18.73	$18.75	$18.70
Purchase #2	$83.95	9.286%	$91.7456	$91.75	$91.75	$91.70
Purchase #3	$77.28	6.642%	$82.4129	$82.41	$82.40	$82.40
Purchase #4	$248.48	13.239%	$281.3763	$281.38	$281.40	$281.40
Purchase #5	$246.45	4.142%	$256.658	$256.66	$256.65	$256.70
Purchase #6	$126.87	4.324%	$132.3559	$132.36	$132.35	$132.40
Purchase #7	$68.35	5.783%	$72.3027	$72.30	$72.30	$72.30
7 purchase totals =	$868.03		$935.5813	$935.59	$935.60	$935.60