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	$104.58	6.600%	$111.4823	$111.48	$111.50	$111.50
Purchase #2	$218.52	5.486%	$230.508	$230.51	$230.50	$230.50
Purchase #3	$16.62	13.568%	$18.875	$18.88	$18.90	$18.90
Purchase #4	$119.78	12.851%	$135.1729	$135.17	$135.15	$135.20
Purchase #5	$42.64	7.807%	$45.9689	$45.97	$45.95	$46.00
Purchase #6	$34.52	5.126%	$36.2895	$36.29	$36.30	$36.30
Purchase #7	$81.71	10.655%	$90.4162	$90.42	$90.40	$90.40
7 purchase totals =	$618.37		$668.7128	$668.72	$668.70	$668.80