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	$141.25	6.203%	$150.0117	$150.01	$150.00	$150.00
Purchase #2	$145.85	9.755%	$160.0777	$160.08	$160.10	$160.10
Purchase #3	$208.55	6.504%	$222.1141	$222.11	$222.10	$222.10
Purchase #4	$42.66	5.184%	$44.8715	$44.87	$44.85	$44.90
Purchase #5	$116.63	9.570%	$127.7915	$127.79	$127.80	$127.80
Purchase #6	$55.29	10.816%	$61.2702	$61.27	$61.25	$61.30
Purchase #7	$122.97	3.760%	$127.5937	$127.59	$127.60	$127.60
7 purchase totals =	$833.20		$893.7304	$893.72	$893.70	$893.80