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	$204.26	8.379%	$221.3749	$221.37	$221.35	$221.40
Purchase #2	$205.54	10.474%	$227.0683	$227.07	$227.05	$227.10
Purchase #3	$91.35	11.524%	$101.8772	$101.88	$101.90	$101.90
Purchase #4	$108.71	8.702%	$118.1699	$118.17	$118.15	$118.20
Purchase #5	$242.74	5.298%	$255.6004	$255.60	$255.60	$255.60
Purchase #6	$70.43	10.847%	$78.0695	$78.07	$78.05	$78.10
Purchase #7	$69.91	11.166%	$77.7162	$77.72	$77.70	$77.70
7 purchase totals =	$992.94		$1,079.8764	$1,079.88	$1,079.80	$1,080.00