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	$245.60	12.168%	$275.4846	$275.48	$275.50	$275.50
Purchase #2	$191.45	5.686%	$202.3358	$202.34	$202.35	$202.30
Purchase #3	$147.46	12.598%	$166.037	$166.04	$166.05	$166.00
Purchase #4	$142.44	4.810%	$149.2914	$149.29	$149.30	$149.30
Purchase #5	$40.40	12.536%	$45.4645	$45.46	$45.45	$45.50
Purchase #6	$196.44	9.283%	$214.6755	$214.68	$214.70	$214.70
Purchase #7	$7.27	12.365%	$8.1689	$8.17	$8.15	$8.20
7 purchase totals =	$971.06		$1,061.4577	$1,061.46	$1,061.50	$1,061.50