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	$56.71	6.687%	$60.5022	$60.50	$60.50	$60.50
Purchase #2	$236.30	3.178%	$243.8096	$243.81	$243.80	$243.80
Purchase #3	$55.54	13.130%	$62.8324	$62.83	$62.85	$62.80
Purchase #4	$129.81	9.139%	$141.6733	$141.67	$141.65	$141.70
Purchase #5	$245.89	4.212%	$256.2469	$256.25	$256.25	$256.20
Purchase #6	$183.79	13.660%	$208.8957	$208.90	$208.90	$208.90
Purchase #7	$91.91	6.474%	$97.8603	$97.86	$97.85	$97.90
7 purchase totals =	$999.95		$1,071.8204	$1,071.82	$1,071.80	$1,071.80