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	$42.53	9.555%	$46.5937	$46.59	$46.60	$46.60
Purchase #2	$39.67	9.802%	$43.5585	$43.56	$43.55	$43.60
Purchase #3	$206.41	11.417%	$229.9758	$229.98	$230.00	$230.00
Purchase #4	$38.58	5.298%	$40.624	$40.62	$40.60	$40.60
Purchase #5	$33.90	10.699%	$37.527	$37.53	$37.55	$37.50
Purchase #6	$156.48	6.126%	$166.066	$166.07	$166.05	$166.10
Purchase #7	$9.51	8.143%	$10.2844	$10.28	$10.30	$10.30
7 purchase totals =	$527.08		$574.6294	$574.63	$574.65	$574.70