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	$11.71	5.633%	$12.3696	$12.37	$12.35	$12.40
Purchase #2	$167.94	4.290%	$175.1446	$175.14	$175.15	$175.10
Purchase #3	$205.42	4.373%	$214.403	$214.40	$214.40	$214.40
Purchase #4	$139.44	12.205%	$156.4587	$156.46	$156.45	$156.50
Purchase #5	$236.52	11.333%	$263.3248	$263.32	$263.30	$263.30
Purchase #6	$226.42	10.561%	$250.3322	$250.33	$250.35	$250.30
Purchase #7	$17.60	7.231%	$18.8727	$18.87	$18.85	$18.90
7 purchase totals =	$1,005.05		$1,090.9056	$1,090.89	$1,090.85	$1,090.90