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	$46.33	12.111%	$51.941	$51.94	$51.95	$51.90
Purchase #2	$186.41	13.482%	$211.5418	$211.54	$211.55	$211.50
Purchase #3	$54.45	8.631%	$59.1496	$59.15	$59.15	$59.10
Purchase #4	$71.96	11.578%	$80.2915	$80.29	$80.30	$80.30
Purchase #5	$9.45	9.332%	$10.3319	$10.33	$10.35	$10.30
Purchase #6	$31.92	8.647%	$34.6801	$34.68	$34.70	$34.70
Purchase #7	$55.72	10.816%	$61.7467	$61.75	$61.75	$61.70
7 purchase totals =	$456.24		$509.6826	$509.68	$509.75	$509.50