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	$73.68	6.717%	$78.6291	$78.63	$78.65	$78.60
Purchase #2	$109.92	13.542%	$124.8054	$124.81	$124.80	$124.80
Purchase #3	$127.28	4.667%	$133.2202	$133.22	$133.20	$133.20
Purchase #4	$45.62	8.463%	$49.4808	$49.48	$49.50	$49.50
Purchase #5	$246.86	7.115%	$264.4241	$264.42	$264.40	$264.40
Purchase #6	$116.30	9.437%	$127.2752	$127.28	$127.30	$127.30
Purchase #7	$173.41	10.331%	$191.325	$191.33	$191.35	$191.30
7 purchase totals =	$893.07		$969.1598	$969.17	$969.20	$969.10