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	$78.76	7.813%	$84.9135	$84.91	$84.90	$84.90
Purchase #2	$221.76	7.342%	$238.0416	$238.04	$238.05	$238.00
Purchase #3	$130.59	8.251%	$141.365	$141.37	$141.35	$141.40
Purchase #4	$20.58	4.437%	$21.4931	$21.49	$21.50	$21.50
Purchase #5	$111.95	13.468%	$127.0274	$127.03	$127.05	$127.00
Purchase #6	$17.79	4.618%	$18.6115	$18.61	$18.60	$18.60
Purchase #7	$248.83	12.518%	$279.9785	$279.98	$280.00	$280.00
7 purchase totals =	$830.26		$911.4306	$911.43	$911.45	$911.40