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	$34.98	6.815%	$37.3639	$37.36	$37.35	$37.40
Purchase #2	$159.52	11.700%	$178.1838	$178.18	$178.20	$178.20
Purchase #3	$25.91	4.450%	$27.063	$27.06	$27.05	$27.10
Purchase #4	$125.33	13.668%	$142.4601	$142.46	$142.45	$142.50
Purchase #5	$147.35	13.208%	$166.812	$166.81	$166.80	$166.80
Purchase #6	$20.58	4.514%	$21.509	$21.51	$21.50	$21.50
Purchase #7	$36.33	10.770%	$40.2427	$40.24	$40.25	$40.20
7 purchase totals =	$550.00		$613.6345	$613.62	$613.60	$613.70