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	$145.37	10.370%	$160.4449	$160.44	$160.45	$160.40
Purchase #2	$154.39	10.848%	$171.1382	$171.14	$171.15	$171.10
Purchase #3	$79.94	6.668%	$85.2704	$85.27	$85.25	$85.30
Purchase #4	$119.30	10.702%	$132.0675	$132.07	$132.05	$132.10
Purchase #5	$154.62	7.671%	$166.4809	$166.48	$166.50	$166.50
Purchase #6	$77.73	3.111%	$80.1482	$80.15	$80.15	$80.10
Purchase #7	$12.45	4.674%	$13.0319	$13.03	$13.05	$13.00
7 purchase totals =	$743.80		$808.5820	$808.58	$808.60	$808.50