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	$239.67	13.613%	$272.2963	$272.30	$272.30	$272.30
Purchase #2	$39.57	4.834%	$41.4828	$41.48	$41.50	$41.50
Purchase #3	$146.67	9.127%	$160.0566	$160.06	$160.05	$160.10
Purchase #4	$99.29	10.363%	$109.5794	$109.58	$109.60	$109.60
Purchase #5	$156.71	11.407%	$174.5859	$174.59	$174.60	$174.60
Purchase #6	$41.97	11.678%	$46.8713	$46.87	$46.85	$46.90
Purchase #7	$60.95	9.465%	$66.7189	$66.72	$66.70	$66.70
7 purchase totals =	$784.83		$871.5912	$871.60	$871.60	$871.70