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	$9.74	3.117%	$10.0436	$10.04	$10.05	$10.00
Purchase #2	$93.49	7.642%	$100.6345	$100.63	$100.65	$100.60
Purchase #3	$219.90	8.540%	$238.6795	$238.68	$238.70	$238.70
Purchase #4	$60.83	11.480%	$67.8133	$67.81	$67.80	$67.80
Purchase #5	$176.52	11.198%	$196.2867	$196.29	$196.30	$196.30
Purchase #6	$93.31	3.766%	$96.8241	$96.82	$96.80	$96.80
Purchase #7	$52.59	10.402%	$58.0604	$58.06	$58.05	$58.10
7 purchase totals =	$706.38		$768.3421	$768.33	$768.35	$768.30