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	$170.57	8.797%	$185.575	$185.58	$185.60	$185.60
Purchase #2	$155.92	3.337%	$161.1231	$161.12	$161.10	$161.10
Purchase #3	$92.87	12.866%	$104.8187	$104.82	$104.80	$104.80
Purchase #4	$106.88	11.241%	$118.8944	$118.89	$118.90	$118.90
Purchase #5	$169.55	12.533%	$190.7997	$190.80	$190.80	$190.80
Purchase #6	$13.54	11.636%	$15.1155	$15.12	$15.10	$15.10
Purchase #7	$154.98	12.802%	$174.8205	$174.82	$174.80	$174.80
7 purchase totals =	$864.31		$951.1469	$951.15	$951.10	$951.10