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	$220.82	10.235%	$243.4209	$243.42	$243.40	$243.40
Purchase #2	$109.39	13.181%	$123.8087	$123.81	$123.80	$123.80
Purchase #3	$227.69	12.654%	$256.5019	$256.50	$256.50	$256.50
Purchase #4	$39.99	4.489%	$41.7852	$41.79	$41.80	$41.80
Purchase #5	$172.44	10.195%	$190.0203	$190.02	$190.00	$190.00
Purchase #6	$227.40	9.847%	$249.7921	$249.79	$249.80	$249.80
Purchase #7	$19.40	12.221%	$21.7709	$21.77	$21.75	$21.80
7 purchase totals =	$1,017.13		$1,127.1000	$1,127.10	$1,127.05	$1,127.10