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	$78.78	12.508%	$88.6338	$88.63	$88.65	$88.60
Purchase #2	$29.35	7.618%	$31.5859	$31.59	$31.60	$31.60
Purchase #3	$18.93	8.869%	$20.6089	$20.61	$20.60	$20.60
Purchase #4	$97.65	7.475%	$104.9493	$104.95	$104.95	$104.90
Purchase #5	$128.82	6.558%	$137.268	$137.27	$137.25	$137.30
Purchase #6	$72.83	5.765%	$77.0286	$77.03	$77.05	$77.00
Purchase #7	$145.32	4.103%	$151.2825	$151.28	$151.30	$151.30
7 purchase totals =	$571.68		$611.3570	$611.36	$611.40	$611.30