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	$179.57	5.598%	$189.6223	$189.62	$189.60	$189.60
Purchase #2	$65.98	4.786%	$69.1378	$69.14	$69.15	$69.10
Purchase #3	$35.82	13.313%	$40.5887	$40.59	$40.60	$40.60
Purchase #4	$120.95	8.103%	$130.7506	$130.75	$130.75	$130.80
Purchase #5	$123.44	6.361%	$131.292	$131.29	$131.30	$131.30
Purchase #6	$55.26	7.218%	$59.2487	$59.25	$59.25	$59.20
Purchase #7	$206.89	9.852%	$227.2728	$227.27	$227.25	$227.30
7 purchase totals =	$787.91		$847.9129	$847.91	$847.90	$847.90