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	$120.86	5.236%	$127.1882	$127.19	$127.20	$127.20
Purchase #2	$153.59	5.625%	$162.2294	$162.23	$162.25	$162.20
Purchase #3	$25.98	9.221%	$28.3756	$28.38	$28.40	$28.40
Purchase #4	$125.62	13.257%	$142.2734	$142.27	$142.25	$142.30
Purchase #5	$154.39	3.403%	$159.6439	$159.64	$159.65	$159.60
Purchase #6	$137.77	8.561%	$149.5645	$149.56	$149.55	$149.60
Purchase #7	$92.56	12.170%	$103.8246	$103.82	$103.80	$103.80
7 purchase totals =	$810.77		$873.0996	$873.09	$873.10	$873.10