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	$79.96	12.549%	$89.9942	$89.99	$90.00	$90.00
Purchase #2	$211.68	12.259%	$237.6299	$237.63	$237.65	$237.60
Purchase #3	$64.49	4.263%	$67.2392	$67.24	$67.25	$67.20
Purchase #4	$137.45	10.458%	$151.8245	$151.82	$151.80	$151.80
Purchase #5	$201.65	10.392%	$222.6055	$222.61	$222.60	$222.60
Purchase #6	$106.85	5.528%	$112.7567	$112.76	$112.75	$112.80
Purchase #7	$127.54	11.748%	$142.5234	$142.52	$142.50	$142.50
7 purchase totals =	$929.62		$1,024.5734	$1,024.57	$1,024.55	$1,024.50