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	$247.99	4.130%	$258.232	$258.23	$258.25	$258.20
Purchase #2	$52.25	9.682%	$57.3088	$57.31	$57.30	$57.30
Purchase #3	$227.89	11.767%	$254.7058	$254.71	$254.70	$254.70
Purchase #4	$111.53	4.759%	$116.8377	$116.84	$116.85	$116.80
Purchase #5	$79.68	12.104%	$89.3245	$89.32	$89.30	$89.30
Purchase #6	$171.57	7.232%	$183.9779	$183.98	$184.00	$184.00
Purchase #7	$86.28	4.232%	$89.9314	$89.93	$89.95	$89.90
7 purchase totals =	$977.19		$1,050.3181	$1,050.32	$1,050.35	$1,050.20