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	$64.71	7.106%	$69.3083	$69.31	$69.30	$69.30
Purchase #2	$30.94	5.763%	$32.7231	$32.72	$32.70	$32.70
Purchase #3	$237.40	3.574%	$245.8847	$245.88	$245.90	$245.90
Purchase #4	$154.53	7.762%	$166.5246	$166.52	$166.50	$166.50
Purchase #5	$36.26	4.670%	$37.9533	$37.95	$37.95	$38.00
Purchase #6	$100.71	10.805%	$111.5917	$111.59	$111.60	$111.60
Purchase #7	$43.42	7.607%	$46.723	$46.72	$46.70	$46.70
7 purchase totals =	$667.97		$710.7087	$710.69	$710.65	$710.70