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	$25.52	10.708%	$28.2527	$28.25	$28.25	$28.30
Purchase #2	$173.47	3.870%	$180.1833	$180.18	$180.20	$180.20
Purchase #3	$164.80	12.542%	$185.4692	$185.47	$185.45	$185.50
Purchase #4	$58.74	6.588%	$62.6098	$62.61	$62.60	$62.60
Purchase #5	$118.59	9.133%	$129.4208	$129.42	$129.40	$129.40
Purchase #6	$247.56	7.671%	$266.5503	$266.55	$266.55	$266.60
Purchase #7	$130.74	10.510%	$144.4808	$144.48	$144.50	$144.50
7 purchase totals =	$919.42		$996.9669	$996.96	$996.95	$997.10