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	$63.90	9.787%	$70.1539	$70.15	$70.15	$70.20
Purchase #2	$47.71	7.485%	$51.2811	$51.28	$51.30	$51.30
Purchase #3	$109.31	9.174%	$119.3381	$119.34	$119.35	$119.30
Purchase #4	$170.72	13.748%	$194.1906	$194.19	$194.20	$194.20
Purchase #5	$74.53	4.743%	$78.065	$78.07	$78.05	$78.10
Purchase #6	$112.84	3.378%	$116.6517	$116.65	$116.65	$116.70
Purchase #7	$142.82	5.225%	$150.2823	$150.28	$150.30	$150.30
7 purchase totals =	$721.83		$779.9627	$779.96	$780.00	$780.10