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	$134.90	6.830%	$144.1137	$144.11	$144.10	$144.10
Purchase #2	$132.82	7.597%	$142.9103	$142.91	$142.90	$142.90
Purchase #3	$33.33	13.273%	$37.7539	$37.75	$37.75	$37.80
Purchase #4	$53.84	7.849%	$58.0659	$58.07	$58.05	$58.10
Purchase #5	$48.44	7.792%	$52.2144	$52.21	$52.20	$52.20
Purchase #6	$112.92	3.435%	$116.7988	$116.80	$116.80	$116.80
Purchase #7	$37.60	8.577%	$40.825	$40.83	$40.85	$40.80
7 purchase totals =	$553.85		$592.6820	$592.68	$592.65	$592.70