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	$47.45	12.789%	$53.5184	$53.52	$53.50	$53.50
Purchase #2	$13.49	11.344%	$15.0203	$15.02	$15.00	$15.00
Purchase #3	$206.31	7.741%	$222.2805	$222.28	$222.30	$222.30
Purchase #4	$37.32	13.354%	$42.3037	$42.30	$42.30	$42.30
Purchase #5	$30.68	11.735%	$34.2803	$34.28	$34.30	$34.30
Purchase #6	$246.30	10.396%	$271.9053	$271.91	$271.90	$271.90
Purchase #7	$241.96	10.818%	$268.1352	$268.14	$268.15	$268.10
7 purchase totals =	$823.51		$907.4437	$907.45	$907.45	$907.40