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	$69.92	4.181%	$72.8434	$72.84	$72.85	$72.80
Purchase #2	$57.72	8.263%	$62.4894	$62.49	$62.50	$62.50
Purchase #3	$137.32	7.515%	$147.6396	$147.64	$147.65	$147.60
Purchase #4	$13.99	5.836%	$14.8065	$14.81	$14.80	$14.80
Purchase #5	$29.57	9.246%	$32.304	$32.30	$32.30	$32.30
Purchase #6	$127.77	11.825%	$142.8788	$142.88	$142.90	$142.90
Purchase #7	$68.29	12.238%	$76.6473	$76.65	$76.65	$76.60
7 purchase totals =	$504.58		$549.6090	$549.61	$549.65	$549.50