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	$124.61	5.251%	$131.1533	$131.15	$131.15	$131.20
Purchase #2	$179.71	6.507%	$191.4037	$191.40	$191.40	$191.40
Purchase #3	$164.46	13.565%	$186.769	$186.77	$186.75	$186.80
Purchase #4	$39.73	6.429%	$42.2842	$42.28	$42.30	$42.30
Purchase #5	$241.83	5.702%	$255.6191	$255.62	$255.60	$255.60
Purchase #6	$57.78	13.764%	$65.7328	$65.73	$65.75	$65.70
Purchase #7	$42.59	10.847%	$47.2097	$47.21	$47.20	$47.20
7 purchase totals =	$850.71		$920.1718	$920.16	$920.15	$920.20