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	$90.70	9.691%	$99.4897	$99.49	$99.50	$99.50
Purchase #2	$66.48	5.646%	$70.2335	$70.23	$70.25	$70.20
Purchase #3	$66.76	13.190%	$75.5656	$75.57	$75.55	$75.60
Purchase #4	$122.99	12.408%	$138.2506	$138.25	$138.25	$138.30
Purchase #5	$121.68	4.499%	$127.1544	$127.15	$127.15	$127.20
Purchase #6	$26.76	5.833%	$28.3209	$28.32	$28.30	$28.30
Purchase #7	$71.94	8.857%	$78.3117	$78.31	$78.30	$78.30
7 purchase totals =	$567.31		$617.3264	$617.32	$617.30	$617.40