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	$25.89	10.605%	$28.6356	$28.64	$28.65	$28.60
Purchase #2	$49.64	8.151%	$53.6862	$53.69	$53.70	$53.70
Purchase #3	$229.57	11.213%	$255.3117	$255.31	$255.30	$255.30
Purchase #4	$136.66	11.737%	$152.6998	$152.70	$152.70	$152.70
Purchase #5	$49.53	6.445%	$52.7222	$52.72	$52.70	$52.70
Purchase #6	$124.33	12.162%	$139.451	$139.45	$139.45	$139.50
Purchase #7	$155.89	5.446%	$164.3798	$164.38	$164.40	$164.40
7 purchase totals =	$771.51		$846.8863	$846.89	$846.90	$846.90