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	$25.52	11.104%	$28.3537	$28.35	$28.35	$28.40
Purchase #2	$210.72	11.628%	$235.2225	$235.22	$235.20	$235.20
Purchase #3	$222.64	12.322%	$250.0737	$250.07	$250.05	$250.10
Purchase #4	$57.72	13.174%	$65.324	$65.32	$65.30	$65.30
Purchase #5	$154.78	11.226%	$172.1556	$172.16	$172.15	$172.20
Purchase #6	$63.28	4.461%	$66.1029	$66.10	$66.10	$66.10
Purchase #7	$91.56	10.365%	$101.0502	$101.05	$101.05	$101.10
7 purchase totals =	$826.22		$918.2826	$918.27	$918.20	$918.40