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	$57.59	11.861%	$64.4207	$64.42	$64.40	$64.40
Purchase #2	$159.92	5.161%	$168.1735	$168.17	$168.15	$168.20
Purchase #3	$160.59	11.168%	$178.5247	$178.52	$178.50	$178.50
Purchase #4	$175.30	9.400%	$191.7782	$191.78	$191.80	$191.80
Purchase #5	$197.44	12.844%	$222.7992	$222.80	$222.80	$222.80
Purchase #6	$97.95	11.162%	$108.8832	$108.88	$108.90	$108.90
Purchase #7	$53.88	13.652%	$61.2357	$61.24	$61.25	$61.20
7 purchase totals =	$902.67		$995.8152	$995.81	$995.80	$995.80