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	$53.70	8.798%	$58.4245	$58.42	$58.40	$58.40
Purchase #2	$136.91	8.450%	$148.4789	$148.48	$148.50	$148.50
Purchase #3	$83.89	8.194%	$90.7639	$90.76	$90.75	$90.80
Purchase #4	$108.94	6.583%	$116.1115	$116.11	$116.10	$116.10
Purchase #5	$40.58	11.531%	$45.2593	$45.26	$45.25	$45.30
Purchase #6	$174.53	5.551%	$184.2182	$184.22	$184.20	$184.20
Purchase #7	$162.93	3.405%	$168.4778	$168.48	$168.50	$168.50
7 purchase totals =	$761.48		$811.7341	$811.73	$811.70	$811.80