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	$28.42	13.119%	$32.1484	$32.15	$32.15	$32.10
Purchase #2	$39.71	7.123%	$42.5385	$42.54	$42.55	$42.50
Purchase #3	$105.80	6.168%	$112.3257	$112.33	$112.35	$112.30
Purchase #4	$79.39	8.789%	$86.3676	$86.37	$86.35	$86.40
Purchase #5	$192.86	8.332%	$208.9291	$208.93	$208.95	$208.90
Purchase #6	$227.45	12.230%	$255.2671	$255.27	$255.25	$255.30
Purchase #7	$228.30	4.337%	$238.2014	$238.20	$238.20	$238.20
7 purchase totals =	$901.93		$975.7778	$975.79	$975.80	$975.70