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	$71.54	13.751%	$81.3775	$81.38	$81.40	$81.40
Purchase #2	$165.51	9.124%	$180.6111	$180.61	$180.60	$180.60
Purchase #3	$23.50	4.683%	$24.6005	$24.60	$24.60	$24.60
Purchase #4	$93.85	9.778%	$103.0267	$103.03	$103.05	$103.00
Purchase #5	$40.71	6.103%	$43.1945	$43.19	$43.20	$43.20
Purchase #6	$41.27	10.116%	$45.4449	$45.44	$45.45	$45.40
Purchase #7	$70.34	10.744%	$77.8973	$77.90	$77.90	$77.90
7 purchase totals =	$506.72		$556.1525	$556.15	$556.20	$556.10