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	$120.59	5.739%	$127.5107	$127.51	$127.50	$127.50
Purchase #2	$221.61	10.740%	$245.4109	$245.41	$245.40	$245.40
Purchase #3	$78.43	4.659%	$82.0841	$82.08	$82.10	$82.10
Purchase #4	$75.68	4.623%	$79.1787	$79.18	$79.20	$79.20
Purchase #5	$23.77	3.142%	$24.5169	$24.52	$24.50	$24.50
Purchase #6	$102.61	12.805%	$115.7492	$115.75	$115.75	$115.70
Purchase #7	$120.80	5.159%	$127.0321	$127.03	$127.05	$127.00
7 purchase totals =	$743.49		$801.4826	$801.48	$801.50	$801.40