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	$37.87	12.713%	$42.6844	$42.68	$42.70	$42.70
Purchase #2	$108.80	3.159%	$112.237	$112.24	$112.25	$112.20
Purchase #3	$91.78	3.404%	$94.9042	$94.90	$94.90	$94.90
Purchase #4	$20.70	5.798%	$21.9002	$21.90	$21.90	$21.90
Purchase #5	$164.59	3.717%	$170.7078	$170.71	$170.70	$170.70
Purchase #6	$221.37	11.764%	$247.412	$247.41	$247.40	$247.40
Purchase #7	$212.58	12.233%	$238.5849	$238.58	$238.60	$238.60
7 purchase totals =	$857.69		$928.4305	$928.42	$928.45	$928.40