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	$109.76	13.255%	$124.3087	$124.31	$124.30	$124.30
Purchase #2	$109.47	8.565%	$118.8461	$118.85	$118.85	$118.80
Purchase #3	$29.43	13.858%	$33.5084	$33.51	$33.50	$33.50
Purchase #4	$42.97	7.684%	$46.2718	$46.27	$46.25	$46.30
Purchase #5	$203.82	6.654%	$217.3822	$217.38	$217.40	$217.40
Purchase #6	$79.65	11.153%	$88.5334	$88.53	$88.55	$88.50
Purchase #7	$112.95	13.165%	$127.8199	$127.82	$127.80	$127.80
7 purchase totals =	$688.05		$756.6705	$756.67	$756.65	$756.60