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	$42.88	4.408%	$44.7702	$44.77	$44.75	$44.80
Purchase #2	$55.78	3.863%	$57.9348	$57.93	$57.95	$57.90
Purchase #3	$192.69	10.514%	$212.9494	$212.95	$212.95	$212.90
Purchase #4	$46.28	13.485%	$52.5209	$52.52	$52.50	$52.50
Purchase #5	$161.69	4.753%	$169.3751	$169.38	$169.40	$169.40
Purchase #6	$185.99	5.537%	$196.2883	$196.29	$196.30	$196.30
Purchase #7	$233.93	9.570%	$256.3171	$256.32	$256.30	$256.30
7 purchase totals =	$919.24		$990.1558	$990.16	$990.15	$990.10