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	$31.91	8.618%	$34.66	$34.66	$34.65	$34.70
Purchase #2	$162.70	10.431%	$179.6712	$179.67	$179.65	$179.70
Purchase #3	$36.54	7.693%	$39.351	$39.35	$39.35	$39.40
Purchase #4	$156.33	10.310%	$172.4476	$172.45	$172.45	$172.40
Purchase #5	$64.30	12.558%	$72.3748	$72.37	$72.35	$72.40
Purchase #6	$220.79	10.783%	$244.5978	$244.60	$244.60	$244.60
Purchase #7	$249.25	3.654%	$258.3576	$258.36	$258.35	$258.40
7 purchase totals =	$921.82		$1,001.4600	$1,001.46	$1,001.40	$1,001.60