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	$124.67	12.243%	$139.9333	$139.93	$139.95	$139.90
Purchase #2	$195.46	8.185%	$211.4584	$211.46	$211.45	$211.50
Purchase #3	$72.46	8.865%	$78.8836	$78.88	$78.90	$78.90
Purchase #4	$46.84	8.494%	$50.8186	$50.82	$50.80	$50.80
Purchase #5	$49.67	8.446%	$53.8651	$53.87	$53.85	$53.90
Purchase #6	$77.85	13.233%	$88.1519	$88.15	$88.15	$88.20
Purchase #7	$200.94	9.729%	$220.4895	$220.49	$220.50	$220.50
7 purchase totals =	$767.89		$843.6004	$843.60	$843.60	$843.70