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	$38.80	9.586%	$42.5194	$42.52	$42.50	$42.50
Purchase #2	$200.90	12.270%	$225.5504	$225.55	$225.55	$225.60
Purchase #3	$243.91	4.731%	$255.4494	$255.45	$255.45	$255.40
Purchase #4	$178.90	7.212%	$191.8023	$191.80	$191.80	$191.80
Purchase #5	$115.53	10.395%	$127.5393	$127.54	$127.55	$127.50
Purchase #6	$233.40	13.833%	$265.6862	$265.69	$265.70	$265.70
Purchase #7	$197.71	11.651%	$220.7452	$220.75	$220.75	$220.70
7 purchase totals =	$1,209.15		$1,329.2922	$1,329.30	$1,329.30	$1,329.20