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	$46.51	12.720%	$52.4261	$52.43	$52.45	$52.40
Purchase #2	$28.62	12.765%	$32.2733	$32.27	$32.25	$32.30
Purchase #3	$108.38	7.537%	$116.5486	$116.55	$116.55	$116.50
Purchase #4	$31.70	3.596%	$32.8399	$32.84	$32.85	$32.80
Purchase #5	$42.74	10.262%	$47.126	$47.13	$47.15	$47.10
Purchase #6	$11.83	7.270%	$12.69	$12.69	$12.70	$12.70
Purchase #7	$196.34	4.142%	$204.4724	$204.47	$204.45	$204.50
7 purchase totals =	$466.12		$498.3763	$498.38	$498.40	$498.30