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	$229.61	8.339%	$248.7572	$248.76	$248.75	$248.80
Purchase #2	$146.33	9.692%	$160.5123	$160.51	$160.50	$160.50
Purchase #3	$247.57	4.291%	$258.1932	$258.19	$258.20	$258.20
Purchase #4	$58.90	12.343%	$66.17	$66.17	$66.15	$66.20
Purchase #5	$84.91	5.382%	$89.4799	$89.48	$89.50	$89.50
Purchase #6	$72.41	13.679%	$82.315	$82.32	$82.30	$82.30
Purchase #7	$50.99	12.372%	$57.2985	$57.30	$57.30	$57.30
7 purchase totals =	$890.72		$962.7261	$962.73	$962.70	$962.80