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	$124.30	3.178%	$128.2503	$128.25	$128.25	$128.30
Purchase #2	$105.66	13.181%	$119.587	$119.59	$119.60	$119.60
Purchase #3	$124.74	5.106%	$131.1092	$131.11	$131.10	$131.10
Purchase #4	$50.79	5.806%	$53.7389	$53.74	$53.75	$53.70
Purchase #5	$119.80	6.675%	$127.7967	$127.80	$127.80	$127.80
Purchase #6	$17.53	4.216%	$18.2691	$18.27	$18.25	$18.30
Purchase #7	$128.40	4.612%	$134.3218	$134.32	$134.30	$134.30
7 purchase totals =	$671.22		$713.0730	$713.08	$713.05	$713.10