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	$230.91	3.415%	$238.7956	$238.80	$238.80	$238.80
Purchase #2	$247.80	8.384%	$268.5756	$268.58	$268.60	$268.60
Purchase #3	$34.92	6.289%	$37.1161	$37.12	$37.10	$37.10
Purchase #4	$97.27	11.340%	$108.3004	$108.30	$108.30	$108.30
Purchase #5	$53.58	3.575%	$55.4955	$55.50	$55.50	$55.50
Purchase #6	$166.95	5.854%	$176.7233	$176.72	$176.70	$176.70
Purchase #7	$82.59	10.106%	$90.9365	$90.94	$90.95	$90.90
7 purchase totals =	$914.02		$975.9430	$975.96	$975.95	$975.90