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	$17.51	7.330%	$18.7935	$18.79	$18.80	$18.80
Purchase #2	$247.57	12.810%	$279.2837	$279.28	$279.30	$279.30
Purchase #3	$89.69	12.115%	$100.5559	$100.56	$100.55	$100.60
Purchase #4	$10.86	3.474%	$11.2373	$11.24	$11.25	$11.20
Purchase #5	$175.77	5.237%	$184.9751	$184.98	$185.00	$185.00
Purchase #6	$204.84	10.758%	$226.8767	$226.88	$226.90	$226.90
Purchase #7	$203.69	13.341%	$230.8643	$230.86	$230.85	$230.90
7 purchase totals =	$949.93		$1,052.5865	$1,052.59	$1,052.65	$1,052.70