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	$72.40	8.767%	$78.7473	$78.75	$78.75	$78.70
Purchase #2	$83.40	3.526%	$86.3407	$86.34	$86.35	$86.30
Purchase #3	$211.48	5.391%	$222.8809	$222.88	$222.90	$222.90
Purchase #4	$40.92	12.480%	$46.0268	$46.03	$46.05	$46.00
Purchase #5	$51.59	13.256%	$58.4288	$58.43	$58.45	$58.40
Purchase #6	$247.55	5.874%	$262.0911	$262.09	$262.10	$262.10
Purchase #7	$21.51	3.432%	$22.2482	$22.25	$22.25	$22.20
7 purchase totals =	$728.85		$776.7638	$776.77	$776.85	$776.60