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	$165.99	8.760%	$180.5307	$180.53	$180.55	$180.50
Purchase #2	$169.69	10.359%	$187.2682	$187.27	$187.25	$187.30
Purchase #3	$36.72	5.212%	$38.6338	$38.63	$38.65	$38.60
Purchase #4	$73.80	11.601%	$82.3615	$82.36	$82.35	$82.40
Purchase #5	$48.40	4.339%	$50.5001	$50.50	$50.50	$50.50
Purchase #6	$58.79	4.531%	$61.4538	$61.45	$61.45	$61.50
Purchase #7	$17.45	3.333%	$18.0316	$18.03	$18.05	$18.00
7 purchase totals =	$570.84		$618.7797	$618.77	$618.80	$618.80