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	$52.71	6.641%	$56.2105	$56.21	$56.20	$56.20
Purchase #2	$222.43	5.226%	$234.0542	$234.05	$234.05	$234.10
Purchase #3	$70.58	4.631%	$73.8486	$73.85	$73.85	$73.80
Purchase #4	$155.81	6.190%	$165.4546	$165.45	$165.45	$165.50
Purchase #5	$233.30	9.443%	$255.3305	$255.33	$255.35	$255.30
Purchase #6	$105.71	3.573%	$109.487	$109.49	$109.50	$109.50
Purchase #7	$41.40	10.701%	$45.8302	$45.83	$45.85	$45.80
7 purchase totals =	$881.94		$940.2156	$940.21	$940.25	$940.20