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	$101.63	13.724%	$115.5777	$115.58	$115.60	$115.60
Purchase #2	$245.76	13.512%	$278.9671	$278.97	$278.95	$279.00
Purchase #3	$198.53	12.257%	$222.8638	$222.86	$222.85	$222.90
Purchase #4	$160.73	4.617%	$168.1509	$168.15	$168.15	$168.20
Purchase #5	$72.96	4.544%	$76.2753	$76.28	$76.30	$76.30
Purchase #6	$230.39	12.648%	$259.5297	$259.53	$259.55	$259.50
Purchase #7	$149.58	11.298%	$166.4795	$166.48	$166.50	$166.50
7 purchase totals =	$1,159.58		$1,287.8440	$1,287.85	$1,287.90	$1,288.00