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	$17.62	11.170%	$19.5882	$19.59	$19.60	$19.60
Purchase #2	$136.39	6.538%	$145.3072	$145.31	$145.30	$145.30
Purchase #3	$51.48	5.110%	$54.1106	$54.11	$54.10	$54.10
Purchase #4	$50.26	10.605%	$55.5901	$55.59	$55.60	$55.60
Purchase #5	$49.56	8.607%	$53.8256	$53.83	$53.85	$53.80
Purchase #6	$225.43	8.356%	$244.2669	$244.27	$244.25	$244.30
Purchase #7	$61.96	4.712%	$64.8796	$64.88	$64.90	$64.90
7 purchase totals =	$592.70		$637.5682	$637.58	$637.60	$637.60