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	$187.58	13.184%	$212.3105	$212.31	$212.30	$212.30
Purchase #2	$132.33	7.838%	$142.702	$142.70	$142.70	$142.70
Purchase #3	$80.66	10.386%	$89.0373	$89.04	$89.05	$89.00
Purchase #4	$103.50	8.623%	$112.4248	$112.42	$112.40	$112.40
Purchase #5	$121.76	4.493%	$127.2307	$127.23	$127.25	$127.20
Purchase #6	$210.55	13.688%	$239.3701	$239.37	$239.35	$239.40
Purchase #7	$123.28	5.250%	$129.7522	$129.75	$129.75	$129.80
7 purchase totals =	$959.66		$1,052.8276	$1,052.82	$1,052.80	$1,052.80