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	$115.35	10.850%	$127.8655	$127.87	$127.85	$127.90
Purchase #2	$51.38	10.577%	$56.8145	$56.81	$56.80	$56.80
Purchase #3	$114.42	11.743%	$127.8563	$127.86	$127.85	$127.90
Purchase #4	$234.80	8.624%	$255.0492	$255.05	$255.05	$255.00
Purchase #5	$182.95	4.578%	$191.3255	$191.33	$191.35	$191.30
Purchase #6	$92.89	10.660%	$102.7921	$102.79	$102.80	$102.80
Purchase #7	$219.51	6.782%	$234.3972	$234.40	$234.40	$234.40
7 purchase totals =	$1,011.30		$1,096.1003	$1,096.11	$1,096.10	$1,096.10