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	$113.88	7.129%	$121.9985	$122.00	$122.00	$122.00
Purchase #2	$219.72	5.398%	$231.5805	$231.58	$231.60	$231.60
Purchase #3	$41.78	6.339%	$44.4284	$44.43	$44.45	$44.40
Purchase #4	$115.65	10.612%	$127.9228	$127.92	$127.90	$127.90
Purchase #5	$213.35	11.811%	$238.5488	$238.55	$238.55	$238.50
Purchase #6	$50.31	12.595%	$56.6465	$56.65	$56.65	$56.60
Purchase #7	$121.52	4.845%	$127.4076	$127.41	$127.40	$127.40
7 purchase totals =	$876.21		$948.5331	$948.54	$948.55	$948.40