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	$26.45	6.461%	$28.1589	$28.16	$28.15	$28.20
Purchase #2	$143.34	7.280%	$153.7752	$153.78	$153.80	$153.80
Purchase #3	$63.91	12.409%	$71.8406	$71.84	$71.85	$71.80
Purchase #4	$246.54	5.407%	$259.8704	$259.87	$259.85	$259.90
Purchase #5	$104.72	9.583%	$114.7553	$114.76	$114.75	$114.80
Purchase #6	$56.52	5.558%	$59.6614	$59.66	$59.65	$59.70
Purchase #7	$212.52	7.551%	$228.5674	$228.57	$228.55	$228.60
7 purchase totals =	$854.00		$916.6292	$916.64	$916.60	$916.80