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	$151.82	11.223%	$168.8588	$168.86	$168.85	$168.90
Purchase #2	$178.80	11.221%	$198.8631	$198.86	$198.85	$198.90
Purchase #3	$21.41	13.192%	$24.2344	$24.23	$24.25	$24.20
Purchase #4	$152.46	5.321%	$160.5724	$160.57	$160.55	$160.60
Purchase #5	$145.35	4.420%	$151.7745	$151.77	$151.75	$151.80
Purchase #6	$133.55	4.390%	$139.4128	$139.41	$139.40	$139.40
Purchase #7	$36.56	11.784%	$40.8682	$40.87	$40.85	$40.90
7 purchase totals =	$819.95		$884.5842	$884.57	$884.50	$884.70