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	$67.25	7.256%	$72.1297	$72.13	$72.15	$72.10
Purchase #2	$220.55	11.846%	$246.6764	$246.68	$246.70	$246.70
Purchase #3	$233.38	9.283%	$255.0447	$255.04	$255.05	$255.00
Purchase #4	$23.75	3.552%	$24.5936	$24.59	$24.60	$24.60
Purchase #5	$68.73	12.472%	$77.302	$77.30	$77.30	$77.30
Purchase #6	$27.51	6.814%	$29.3845	$29.38	$29.40	$29.40
Purchase #7	$100.43	9.277%	$109.7469	$109.75	$109.75	$109.70
7 purchase totals =	$741.60		$814.8778	$814.87	$814.95	$814.80