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	$53.52	5.563%	$56.4973	$56.50	$56.50	$56.50
Purchase #2	$124.73	6.726%	$133.1193	$133.12	$133.10	$133.10
Purchase #3	$150.81	10.402%	$166.4973	$166.50	$166.50	$166.50
Purchase #4	$114.68	11.108%	$127.4187	$127.42	$127.40	$127.40
Purchase #5	$30.27	4.559%	$31.65	$31.65	$31.65	$31.70
Purchase #6	$88.85	9.116%	$96.9496	$96.95	$96.95	$96.90
Purchase #7	$86.91	4.335%	$90.6775	$90.68	$90.70	$90.70
7 purchase totals =	$649.77		$702.8097	$702.82	$702.80	$702.80