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	$166.44	7.834%	$179.4789	$179.48	$179.50	$179.50
Purchase #2	$129.55	13.582%	$147.1455	$147.15	$147.15	$147.10
Purchase #3	$83.39	8.303%	$90.3139	$90.31	$90.30	$90.30
Purchase #4	$25.35	13.134%	$28.6795	$28.68	$28.70	$28.70
Purchase #5	$245.86	10.687%	$272.1351	$272.14	$272.15	$272.10
Purchase #6	$50.31	7.802%	$54.2352	$54.24	$54.25	$54.20
Purchase #7	$208.28	4.783%	$218.242	$218.24	$218.25	$218.20
7 purchase totals =	$909.18		$990.2301	$990.24	$990.30	$990.10