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	$250.90	11.116%	$278.79	$278.79	$278.80	$278.80
Purchase #2	$72.77	8.422%	$78.8987	$78.90	$78.90	$78.90
Purchase #3	$24.83	7.509%	$26.6945	$26.69	$26.70	$26.70
Purchase #4	$39.89	10.108%	$43.9221	$43.92	$43.90	$43.90
Purchase #5	$50.66	11.654%	$56.5639	$56.56	$56.55	$56.60
Purchase #6	$47.66	9.474%	$52.1753	$52.18	$52.20	$52.20
Purchase #7	$90.95	10.222%	$100.2469	$100.25	$100.25	$100.20
7 purchase totals =	$577.66		$637.2914	$637.29	$637.30	$637.30