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	$189.88	5.156%	$199.6702	$199.67	$199.65	$199.70
Purchase #2	$76.26	3.573%	$78.9848	$78.98	$79.00	$79.00
Purchase #3	$67.40	7.755%	$72.6269	$72.63	$72.65	$72.60
Purchase #4	$29.33	10.160%	$32.3099	$32.31	$32.30	$32.30
Purchase #5	$151.32	9.763%	$166.0934	$166.09	$166.10	$166.10
Purchase #6	$20.66	3.526%	$21.3885	$21.39	$21.40	$21.40
Purchase #7	$15.87	10.749%	$17.5759	$17.58	$17.60	$17.60
7 purchase totals =	$550.72		$588.6496	$588.65	$588.70	$588.70