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	$54.30	6.394%	$57.7719	$57.77	$57.75	$57.80
Purchase #2	$86.86	4.608%	$90.8625	$90.86	$90.85	$90.90
Purchase #3	$79.83	13.168%	$90.342	$90.34	$90.35	$90.30
Purchase #4	$151.87	4.225%	$158.2865	$158.29	$158.30	$158.30
Purchase #5	$50.32	11.568%	$56.141	$56.14	$56.15	$56.10
Purchase #6	$175.33	7.766%	$188.9461	$188.95	$188.95	$188.90
Purchase #7	$132.96	7.196%	$142.5278	$142.53	$142.55	$142.50
7 purchase totals =	$731.47		$784.8778	$784.88	$784.90	$784.80