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	$71.42	9.639%	$78.3042	$78.30	$78.30	$78.30
Purchase #2	$107.54	8.419%	$116.5938	$116.59	$116.60	$116.60
Purchase #3	$244.33	11.159%	$271.5948	$271.59	$271.60	$271.60
Purchase #4	$149.27	6.638%	$159.1785	$159.18	$159.20	$159.20
Purchase #5	$223.58	8.381%	$242.3182	$242.32	$242.30	$242.30
Purchase #6	$45.93	7.647%	$49.4423	$49.44	$49.45	$49.40
Purchase #7	$22.88	8.486%	$24.8216	$24.82	$24.80	$24.80
7 purchase totals =	$864.95		$942.2534	$942.24	$942.25	$942.20