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	$223.36	3.121%	$230.3311	$230.33	$230.35	$230.30
Purchase #2	$115.99	9.651%	$127.1842	$127.18	$127.20	$127.20
Purchase #3	$69.56	4.628%	$72.7792	$72.78	$72.80	$72.80
Purchase #4	$115.39	6.799%	$123.2354	$123.24	$123.25	$123.20
Purchase #5	$129.25	10.723%	$143.1095	$143.11	$143.10	$143.10
Purchase #6	$33.36	11.744%	$37.2778	$37.28	$37.30	$37.30
Purchase #7	$37.28	10.745%	$41.2857	$41.29	$41.30	$41.30
7 purchase totals =	$724.19		$775.2029	$775.21	$775.30	$775.20