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	$78.88	6.383%	$83.9149	$83.91	$83.90	$83.90
Purchase #2	$244.83	13.386%	$277.6029	$277.60	$277.60	$277.60
Purchase #3	$115.27	10.517%	$127.3929	$127.39	$127.40	$127.40
Purchase #4	$188.34	9.435%	$206.1099	$206.11	$206.10	$206.10
Purchase #5	$35.69	4.235%	$37.2015	$37.20	$37.20	$37.20
Purchase #6	$98.37	13.326%	$111.4788	$111.48	$111.50	$111.50
Purchase #7	$228.69	5.242%	$240.6779	$240.68	$240.70	$240.70
7 purchase totals =	$990.07		$1,084.3788	$1,084.37	$1,084.40	$1,084.40