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	$134.76	6.395%	$143.3779	$143.38	$143.40	$143.40
Purchase #2	$244.72	7.846%	$263.9207	$263.92	$263.90	$263.90
Purchase #3	$127.37	4.614%	$133.2469	$133.25	$133.25	$133.20
Purchase #4	$25.54	3.647%	$26.4714	$26.47	$26.45	$26.50
Purchase #5	$205.68	8.722%	$223.6194	$223.62	$223.60	$223.60
Purchase #6	$124.40	10.218%	$137.1112	$137.11	$137.10	$137.10
Purchase #7	$116.65	9.282%	$127.4775	$127.48	$127.50	$127.50
7 purchase totals =	$979.12		$1,055.2250	$1,055.23	$1,055.20	$1,055.20