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	$31.48	12.812%	$35.5132	$35.51	$35.50	$35.50
Purchase #2	$28.90	12.367%	$32.4741	$32.47	$32.45	$32.50
Purchase #3	$87.48	10.257%	$96.4528	$96.45	$96.45	$96.50
Purchase #4	$100.52	10.541%	$111.1158	$111.12	$111.10	$111.10
Purchase #5	$153.83	3.299%	$158.9049	$158.90	$158.90	$158.90
Purchase #6	$19.78	11.720%	$22.0982	$22.10	$22.10	$22.10
Purchase #7	$67.90	10.692%	$75.1599	$75.16	$75.15	$75.20
7 purchase totals =	$489.89		$531.7189	$531.71	$531.65	$531.80