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	$76.28	3.426%	$78.8934	$78.89	$78.90	$78.90
Purchase #2	$104.46	7.554%	$112.3509	$112.35	$112.35	$112.40
Purchase #3	$55.62	3.227%	$57.4149	$57.41	$57.40	$57.40
Purchase #4	$244.59	4.193%	$254.8457	$254.85	$254.85	$254.80
Purchase #5	$32.64	12.246%	$36.6371	$36.64	$36.65	$36.60
Purchase #6	$102.44	4.317%	$106.8623	$106.86	$106.85	$106.90
Purchase #7	$34.69	9.149%	$37.8638	$37.86	$37.85	$37.90
7 purchase totals =	$650.72		$684.8681	$684.86	$684.85	$684.90