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	$144.83	9.683%	$158.8539	$158.85	$158.85	$158.90
Purchase #2	$243.32	4.482%	$254.2256	$254.23	$254.25	$254.20
Purchase #3	$165.51	4.408%	$172.8057	$172.81	$172.80	$172.80
Purchase #4	$226.38	12.321%	$254.2723	$254.27	$254.25	$254.30
Purchase #5	$245.76	4.801%	$257.5589	$257.56	$257.55	$257.60
Purchase #6	$124.56	6.613%	$132.7972	$132.80	$132.80	$132.80
Purchase #7	$245.64	12.645%	$276.7012	$276.70	$276.70	$276.70
7 purchase totals =	$1,396.00		$1,507.2148	$1,507.22	$1,507.20	$1,507.30