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	$124.30	13.689%	$141.3154	$141.32	$141.30	$141.30
Purchase #2	$95.87	9.131%	$104.6239	$104.62	$104.60	$104.60
Purchase #3	$52.81	3.209%	$54.5047	$54.50	$54.50	$54.50
Purchase #4	$93.42	8.632%	$101.484	$101.48	$101.50	$101.50
Purchase #5	$29.54	11.827%	$33.0337	$33.03	$33.05	$33.00
Purchase #6	$31.66	6.203%	$33.6239	$33.62	$33.60	$33.60
Purchase #7	$107.69	12.647%	$121.3096	$121.31	$121.30	$121.30
7 purchase totals =	$535.29		$589.8952	$589.88	$589.85	$589.80