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	$127.73	7.743%	$137.6201	$137.62	$137.60	$137.60
Purchase #2	$149.89	11.507%	$167.1378	$167.14	$167.15	$167.10
Purchase #3	$91.46	3.566%	$94.7215	$94.72	$94.70	$94.70
Purchase #4	$48.61	9.368%	$53.1638	$53.16	$53.15	$53.20
Purchase #5	$12.72	5.831%	$13.4617	$13.46	$13.45	$13.50
Purchase #6	$220.93	10.391%	$243.8868	$243.89	$243.90	$243.90
Purchase #7	$159.45	8.541%	$173.0686	$173.07	$173.05	$173.10
7 purchase totals =	$810.79		$883.0603	$883.06	$883.00	$883.10