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	$248.71	10.722%	$275.3767	$275.38	$275.40	$275.40
Purchase #2	$160.89	3.712%	$166.8622	$166.86	$166.85	$166.90
Purchase #3	$43.31	8.129%	$46.8307	$46.83	$46.85	$46.80
Purchase #4	$105.86	6.522%	$112.7642	$112.76	$112.75	$112.80
Purchase #5	$131.87	12.267%	$148.0465	$148.05	$148.05	$148.00
Purchase #6	$106.92	9.191%	$116.747	$116.75	$116.75	$116.70
Purchase #7	$93.39	12.561%	$105.1207	$105.12	$105.10	$105.10
7 purchase totals =	$890.95		$971.7480	$971.75	$971.75	$971.70