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	$52.31	7.763%	$56.3708	$56.37	$56.35	$56.40
Purchase #2	$202.34	12.714%	$228.0655	$228.07	$228.05	$228.10
Purchase #3	$238.35	3.165%	$245.8938	$245.89	$245.90	$245.90
Purchase #4	$97.42	7.860%	$105.0772	$105.08	$105.10	$105.10
Purchase #5	$185.72	10.773%	$205.7276	$205.73	$205.75	$205.70
Purchase #6	$20.26	5.746%	$21.4241	$21.42	$21.40	$21.40
Purchase #7	$238.75	4.371%	$249.1858	$249.19	$249.20	$249.20
7 purchase totals =	$1,035.15		$1,111.7448	$1,111.75	$1,111.75	$1,111.80