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	$139.59	8.793%	$151.8641	$151.86	$151.85	$151.90
Purchase #2	$30.80	9.236%	$33.6447	$33.64	$33.65	$33.60
Purchase #3	$95.70	10.224%	$105.4844	$105.48	$105.50	$105.50
Purchase #4	$63.51	5.564%	$67.0437	$67.04	$67.05	$67.00
Purchase #5	$198.50	12.800%	$223.908	$223.91	$223.90	$223.90
Purchase #6	$123.81	3.781%	$128.4913	$128.49	$128.50	$128.50
Purchase #7	$94.79	5.335%	$99.847	$99.85	$99.85	$99.80
7 purchase totals =	$746.70		$810.2832	$810.27	$810.30	$810.20