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	$44.95	11.291%	$50.0253	$50.03	$50.05	$50.00
Purchase #2	$213.54	11.711%	$238.5477	$238.55	$238.55	$238.50
Purchase #3	$55.75	5.620%	$58.8832	$58.88	$58.90	$58.90
Purchase #4	$48.40	13.430%	$54.9001	$54.90	$54.90	$54.90
Purchase #5	$50.63	11.649%	$56.5279	$56.53	$56.55	$56.50
Purchase #6	$195.48	7.648%	$210.4303	$210.43	$210.45	$210.40
Purchase #7	$160.29	6.816%	$171.2154	$171.22	$171.20	$171.20
7 purchase totals =	$769.04		$840.5299	$840.54	$840.60	$840.40