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	$171.82	9.577%	$188.2752	$188.28	$188.30	$188.30
Purchase #2	$130.95	10.766%	$145.0481	$145.05	$145.05	$145.00
Purchase #3	$65.78	12.627%	$74.086	$74.09	$74.10	$74.10
Purchase #4	$117.86	12.271%	$132.3226	$132.32	$132.30	$132.30
Purchase #5	$139.77	9.406%	$152.9168	$152.92	$152.90	$152.90
Purchase #6	$33.78	9.542%	$37.0033	$37.00	$37.00	$37.00
Purchase #7	$234.27	3.854%	$243.2988	$243.30	$243.30	$243.30
7 purchase totals =	$894.23		$972.9508	$972.96	$972.95	$972.90