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	$17.82	11.380%	$19.8479	$19.85	$19.85	$19.80
Purchase #2	$135.59	10.720%	$150.1252	$150.13	$150.15	$150.10
Purchase #3	$218.32	7.117%	$233.8578	$233.86	$233.85	$233.90
Purchase #4	$94.54	12.205%	$106.0786	$106.08	$106.10	$106.10
Purchase #5	$111.53	9.816%	$122.4778	$122.48	$122.50	$122.50
Purchase #6	$42.40	7.654%	$45.6453	$45.65	$45.65	$45.60
Purchase #7	$49.53	9.505%	$54.2378	$54.24	$54.25	$54.20
7 purchase totals =	$669.73		$732.2704	$732.29	$732.35	$732.20