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	$123.25	10.237%	$135.8671	$135.87	$135.85	$135.90
Purchase #2	$130.87	10.557%	$144.6859	$144.69	$144.70	$144.70
Purchase #3	$54.92	8.417%	$59.5426	$59.54	$59.55	$59.50
Purchase #4	$105.52	5.458%	$111.2793	$111.28	$111.30	$111.30
Purchase #5	$111.41	9.797%	$122.3248	$122.32	$122.30	$122.30
Purchase #6	$147.63	4.374%	$154.0873	$154.09	$154.10	$154.10
Purchase #7	$90.72	7.448%	$97.4768	$97.48	$97.50	$97.50
7 purchase totals =	$764.32		$825.2638	$825.27	$825.30	$825.30