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	$28.45	4.343%	$29.6856	$29.69	$29.70	$29.70
Purchase #2	$28.50	12.791%	$32.1454	$32.15	$32.15	$32.10
Purchase #3	$182.78	4.300%	$190.6395	$190.64	$190.65	$190.60
Purchase #4	$228.96	10.841%	$253.7816	$253.78	$253.80	$253.80
Purchase #5	$98.75	13.752%	$112.3301	$112.33	$112.35	$112.30
Purchase #6	$230.87	12.493%	$259.7126	$259.71	$259.70	$259.70
Purchase #7	$146.34	6.278%	$155.5272	$155.53	$155.55	$155.50
7 purchase totals =	$944.65		$1,033.8220	$1,033.83	$1,033.90	$1,033.70