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	$27.40	7.123%	$29.3517	$29.35	$29.35	$29.40
Purchase #2	$225.91	12.656%	$254.5012	$254.50	$254.50	$254.50
Purchase #3	$96.70	8.714%	$105.1264	$105.13	$105.15	$105.10
Purchase #4	$174.28	5.542%	$183.9386	$183.94	$183.95	$183.90
Purchase #5	$64.49	11.568%	$71.9502	$71.95	$71.95	$72.00
Purchase #6	$151.69	10.444%	$167.5325	$167.53	$167.55	$167.50
Purchase #7	$227.80	7.286%	$244.3975	$244.40	$244.40	$244.40
7 purchase totals =	$968.27		$1,056.7981	$1,056.80	$1,056.85	$1,056.80