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	$144.40	13.828%	$164.3676	$164.37	$164.35	$164.40
Purchase #2	$44.45	11.350%	$49.4951	$49.50	$49.50	$49.50
Purchase #3	$88.73	12.737%	$100.0315	$100.03	$100.05	$100.00
Purchase #4	$102.91	6.491%	$109.5899	$109.59	$109.60	$109.60
Purchase #5	$53.79	12.501%	$60.5143	$60.51	$60.50	$60.50
Purchase #6	$238.90	4.744%	$250.2334	$250.23	$250.25	$250.20
Purchase #7	$58.95	7.850%	$63.5776	$63.58	$63.60	$63.60
7 purchase totals =	$732.13		$797.8094	$797.81	$797.85	$797.80