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	$9.60	10.297%	$10.5885	$10.59	$10.60	$10.60
Purchase #2	$244.86	4.572%	$256.055	$256.06	$256.05	$256.10
Purchase #3	$62.30	8.175%	$67.393	$67.39	$67.40	$67.40
Purchase #4	$219.75	4.142%	$228.852	$228.85	$228.85	$228.90
Purchase #5	$167.39	12.637%	$188.5431	$188.54	$188.55	$188.50
Purchase #6	$73.79	5.114%	$77.5636	$77.56	$77.55	$77.60
Purchase #7	$59.99	4.131%	$62.4682	$62.47	$62.45	$62.50
7 purchase totals =	$837.68		$891.4634	$891.46	$891.45	$891.60