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	$92.44	11.524%	$103.0928	$103.09	$103.10	$103.10
Purchase #2	$124.63	5.291%	$131.2242	$131.22	$131.20	$131.20
Purchase #3	$135.39	7.225%	$145.1719	$145.17	$145.15	$145.20
Purchase #4	$215.75	10.522%	$238.4512	$238.45	$238.45	$238.50
Purchase #5	$236.42	7.625%	$254.447	$254.45	$254.45	$254.40
Purchase #6	$6.38	4.559%	$6.6709	$6.67	$6.65	$6.70
Purchase #7	$19.32	10.805%	$21.4075	$21.41	$21.40	$21.40
7 purchase totals =	$830.33		$900.4655	$900.46	$900.40	$900.50