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	$72.39	11.292%	$80.5643	$80.56	$80.55	$80.60
Purchase #2	$160.66	8.722%	$174.6728	$174.67	$174.65	$174.70
Purchase #3	$206.64	11.609%	$230.6288	$230.63	$230.65	$230.60
Purchase #4	$218.83	6.188%	$232.3712	$232.37	$232.35	$232.40
Purchase #5	$172.52	4.177%	$179.7262	$179.73	$179.75	$179.70
Purchase #6	$128.85	13.557%	$146.3182	$146.32	$146.30	$146.30
Purchase #7	$53.82	10.716%	$59.5874	$59.59	$59.60	$59.60
7 purchase totals =	$1,013.71		$1,103.8689	$1,103.87	$1,103.85	$1,103.90