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	$71.90	8.822%	$78.243	$78.24	$78.25	$78.20
Purchase #2	$97.44	12.636%	$109.7525	$109.75	$109.75	$109.80
Purchase #3	$28.89	13.203%	$32.7043	$32.70	$32.70	$32.70
Purchase #4	$46.43	12.353%	$52.1655	$52.17	$52.15	$52.20
Purchase #5	$243.83	7.699%	$262.6025	$262.60	$262.60	$262.60
Purchase #6	$229.54	5.158%	$241.3797	$241.38	$241.40	$241.40
Purchase #7	$9.41	3.444%	$9.7341	$9.73	$9.75	$9.70
7 purchase totals =	$727.44		$786.5816	$786.57	$786.60	$786.60