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	$88.59	13.181%	$100.267	$100.27	$100.25	$100.30
Purchase #2	$178.51	10.296%	$196.8894	$196.89	$196.90	$196.90
Purchase #3	$17.75	4.610%	$18.5683	$18.57	$18.55	$18.60
Purchase #4	$88.61	6.613%	$94.4698	$94.47	$94.45	$94.50
Purchase #5	$124.72	11.724%	$139.3422	$139.34	$139.35	$139.30
Purchase #6	$96.64	11.718%	$107.9643	$107.96	$107.95	$108.00
Purchase #7	$85.34	10.493%	$94.2947	$94.29	$94.30	$94.30
7 purchase totals =	$680.16		$751.7957	$751.79	$751.75	$751.90