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	$25.84	10.293%	$28.4997	$28.50	$28.50	$28.50
Purchase #2	$214.75	9.325%	$234.7754	$234.78	$234.80	$234.80
Purchase #3	$202.86	6.798%	$216.6504	$216.65	$216.65	$216.70
Purchase #4	$180.91	7.712%	$194.8618	$194.86	$194.85	$194.90
Purchase #5	$48.56	12.145%	$54.4576	$54.46	$54.45	$54.50
Purchase #6	$202.85	8.409%	$219.9077	$219.91	$219.90	$219.90
Purchase #7	$72.62	13.468%	$82.4005	$82.40	$82.40	$82.40
7 purchase totals =	$948.39		$1,031.5531	$1,031.56	$1,031.55	$1,031.70