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	$173.81	8.573%	$188.7107	$188.71	$188.70	$188.70
Purchase #2	$150.72	6.329%	$160.2591	$160.26	$160.25	$160.30
Purchase #3	$89.38	11.126%	$99.3244	$99.32	$99.30	$99.30
Purchase #4	$60.34	9.335%	$65.9727	$65.97	$65.95	$66.00
Purchase #5	$34.31	12.621%	$38.6403	$38.64	$38.65	$38.60
Purchase #6	$105.57	9.329%	$115.4186	$115.42	$115.40	$115.40
Purchase #7	$176.41	5.362%	$185.8691	$185.87	$185.85	$185.90
7 purchase totals =	$790.54		$854.1949	$854.19	$854.10	$854.20