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	$202.31	10.675%	$223.9066	$223.91	$223.90	$223.90
Purchase #2	$123.32	11.248%	$137.191	$137.19	$137.20	$137.20
Purchase #3	$125.97	8.638%	$136.8513	$136.85	$136.85	$136.90
Purchase #4	$103.47	3.629%	$107.2249	$107.22	$107.20	$107.20
Purchase #5	$169.79	5.483%	$179.0996	$179.10	$179.10	$179.10
Purchase #6	$190.92	12.315%	$214.4318	$214.43	$214.45	$214.40
Purchase #7	$133.67	7.556%	$143.7701	$143.77	$143.75	$143.80
7 purchase totals =	$1,049.45		$1,142.4753	$1,142.47	$1,142.45	$1,142.50