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	$46.68	10.793%	$51.7182	$51.72	$51.70	$51.70
Purchase #2	$123.80	12.769%	$139.608	$139.61	$139.60	$139.60
Purchase #3	$115.61	10.642%	$127.9132	$127.91	$127.90	$127.90
Purchase #4	$126.72	3.255%	$130.8447	$130.84	$130.85	$130.80
Purchase #5	$182.91	3.655%	$189.5954	$189.60	$189.60	$189.60
Purchase #6	$36.80	5.332%	$38.7622	$38.76	$38.75	$38.80
Purchase #7	$249.48	10.566%	$275.8401	$275.84	$275.85	$275.80
7 purchase totals =	$882.00		$954.2818	$954.28	$954.25	$954.20