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	$181.26	12.871%	$204.59	$204.59	$204.60	$204.60
Purchase #2	$147.59	3.164%	$152.2597	$152.26	$152.25	$152.30
Purchase #3	$18.38	11.729%	$20.5358	$20.54	$20.55	$20.50
Purchase #4	$133.90	9.491%	$146.6084	$146.61	$146.60	$146.60
Purchase #5	$36.49	10.666%	$40.382	$40.38	$40.40	$40.40
Purchase #6	$147.80	6.356%	$157.1942	$157.19	$157.20	$157.20
Purchase #7	$83.90	12.269%	$94.1937	$94.19	$94.20	$94.20
7 purchase totals =	$749.32		$815.7638	$815.76	$815.80	$815.80