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	$232.45	13.509%	$263.8517	$263.85	$263.85	$263.90
Purchase #2	$147.56	11.626%	$164.7153	$164.72	$164.70	$164.70
Purchase #3	$133.39	12.298%	$149.7943	$149.79	$149.80	$149.80
Purchase #4	$30.32	7.117%	$32.4779	$32.48	$32.50	$32.50
Purchase #5	$44.67	6.191%	$47.4355	$47.44	$47.45	$47.40
Purchase #6	$178.75	4.193%	$186.245	$186.25	$186.25	$186.20
Purchase #7	$37.89	11.718%	$42.33	$42.33	$42.35	$42.30
7 purchase totals =	$805.03		$886.8497	$886.86	$886.90	$886.80