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	$6.70	13.671%	$7.616	$7.62	$7.60	$7.60
Purchase #2	$70.28	3.679%	$72.8656	$72.87	$72.85	$72.90
Purchase #3	$54.50	11.594%	$60.8187	$60.82	$60.80	$60.80
Purchase #4	$59.93	13.208%	$67.8456	$67.85	$67.85	$67.80
Purchase #5	$74.99	6.180%	$79.6244	$79.62	$79.60	$79.60
Purchase #6	$129.72	6.649%	$138.3451	$138.35	$138.35	$138.30
Purchase #7	$89.27	10.112%	$98.297	$98.30	$98.30	$98.30
7 purchase totals =	$485.39		$525.4124	$525.43	$525.35	$525.30