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	$35.77	5.563%	$37.7599	$37.76	$37.75	$37.80
Purchase #2	$146.25	13.628%	$166.181	$166.18	$166.20	$166.20
Purchase #3	$241.96	6.579%	$257.8785	$257.88	$257.90	$257.90
Purchase #4	$217.65	12.218%	$244.2425	$244.24	$244.25	$244.20
Purchase #5	$111.33	11.329%	$123.9426	$123.94	$123.95	$123.90
Purchase #6	$185.94	5.495%	$196.1574	$196.16	$196.15	$196.20
Purchase #7	$49.80	10.833%	$55.1948	$55.19	$55.20	$55.20
7 purchase totals =	$988.70		$1,081.3567	$1,081.35	$1,081.40	$1,081.40