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	$250.82	11.246%	$279.0272	$279.03	$279.05	$279.00
Purchase #2	$18.96	12.563%	$21.3419	$21.34	$21.35	$21.30
Purchase #3	$168.93	6.724%	$180.2889	$180.29	$180.30	$180.30
Purchase #4	$99.77	9.820%	$109.5674	$109.57	$109.55	$109.60
Purchase #5	$64.87	12.334%	$72.8711	$72.87	$72.85	$72.90
Purchase #6	$19.80	9.356%	$21.6525	$21.65	$21.65	$21.70
Purchase #7	$216.57	10.587%	$239.4983	$239.50	$239.50	$239.50
7 purchase totals =	$839.72		$924.2473	$924.25	$924.25	$924.30