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	$63.71	13.553%	$72.3446	$72.34	$72.35	$72.30
Purchase #2	$47.84	6.841%	$51.1127	$51.11	$51.10	$51.10
Purchase #3	$243.85	13.350%	$276.404	$276.40	$276.40	$276.40
Purchase #4	$6.60	13.738%	$7.5067	$7.51	$7.50	$7.50
Purchase #5	$106.59	11.781%	$119.1474	$119.15	$119.15	$119.10
Purchase #6	$57.72	12.191%	$64.7566	$64.76	$64.75	$64.80
Purchase #7	$11.82	3.587%	$12.244	$12.24	$12.25	$12.20
7 purchase totals =	$538.13		$603.5160	$603.51	$603.50	$603.40