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	$82.76	7.401%	$88.8851	$88.89	$88.90	$88.90
Purchase #2	$68.37	11.472%	$76.2134	$76.21	$76.20	$76.20
Purchase #3	$161.65	4.476%	$168.8855	$168.89	$168.90	$168.90
Purchase #4	$214.43	3.436%	$221.7978	$221.80	$221.80	$221.80
Purchase #5	$133.88	13.213%	$151.5696	$151.57	$151.55	$151.60
Purchase #6	$151.31	3.133%	$156.0505	$156.05	$156.05	$156.10
Purchase #7	$125.83	9.834%	$138.2041	$138.20	$138.20	$138.20
7 purchase totals =	$938.23		$1,001.6060	$1,001.61	$1,001.60	$1,001.70