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	$111.55	5.587%	$117.7823	$117.78	$117.80	$117.80
Purchase #2	$23.98	13.716%	$27.2691	$27.27	$27.25	$27.30
Purchase #3	$94.56	9.397%	$103.4458	$103.45	$103.45	$103.40
Purchase #4	$210.29	10.516%	$232.4041	$232.40	$232.40	$232.40
Purchase #5	$140.80	10.288%	$155.2855	$155.29	$155.30	$155.30
Purchase #6	$115.25	10.728%	$127.614	$127.61	$127.60	$127.60
Purchase #7	$37.52	4.755%	$39.3041	$39.30	$39.30	$39.30
7 purchase totals =	$733.95		$803.1049	$803.10	$803.10	$803.10