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	$159.51	5.387%	$168.1028	$168.10	$168.10	$168.10
Purchase #2	$118.42	11.295%	$131.7955	$131.80	$131.80	$131.80
Purchase #3	$207.92	7.191%	$222.8715	$222.87	$222.85	$222.90
Purchase #4	$89.58	6.838%	$95.7055	$95.71	$95.70	$95.70
Purchase #5	$28.55	7.504%	$30.6924	$30.69	$30.70	$30.70
Purchase #6	$83.68	6.367%	$89.0079	$89.01	$89.00	$89.00
Purchase #7	$124.64	5.108%	$131.0066	$131.01	$131.00	$131.00
7 purchase totals =	$812.30		$869.1822	$869.19	$869.15	$869.20