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	$40.51	4.777%	$42.4452	$42.45	$42.45	$42.40
Purchase #2	$155.28	4.853%	$162.8157	$162.82	$162.80	$162.80
Purchase #3	$150.44	9.736%	$165.0868	$165.09	$165.10	$165.10
Purchase #4	$117.69	4.634%	$123.1438	$123.14	$123.15	$123.10
Purchase #5	$9.50	8.214%	$10.2803	$10.28	$10.30	$10.30
Purchase #6	$173.56	10.275%	$191.3933	$191.39	$191.40	$191.40
Purchase #7	$16.46	7.483%	$17.6917	$17.69	$17.70	$17.70
7 purchase totals =	$663.44		$712.8568	$712.86	$712.90	$712.80