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	$80.84	11.224%	$89.9135	$89.91	$89.90	$89.90
Purchase #2	$146.91	10.538%	$162.3914	$162.39	$162.40	$162.40
Purchase #3	$181.45	12.605%	$204.3218	$204.32	$204.30	$204.30
Purchase #4	$58.59	8.366%	$63.4916	$63.49	$63.50	$63.50
Purchase #5	$68.68	4.291%	$71.6271	$71.63	$71.65	$71.60
Purchase #6	$93.50	10.608%	$103.4185	$103.42	$103.40	$103.40
Purchase #7	$61.85	4.209%	$64.4533	$64.45	$64.45	$64.50
7 purchase totals =	$691.82		$759.6172	$759.61	$759.60	$759.60