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	$129.81	5.462%	$136.9002	$136.90	$136.90	$136.90
Purchase #2	$168.63	4.514%	$176.242	$176.24	$176.25	$176.20
Purchase #3	$50.63	4.455%	$52.8856	$52.89	$52.90	$52.90
Purchase #4	$14.49	12.428%	$16.2908	$16.29	$16.30	$16.30
Purchase #5	$200.89	8.146%	$217.2545	$217.25	$217.25	$217.30
Purchase #6	$83.85	7.583%	$90.2083	$90.21	$90.20	$90.20
Purchase #7	$107.35	3.717%	$111.3402	$111.34	$111.35	$111.30
7 purchase totals =	$755.65		$801.1216	$801.12	$801.15	$801.10