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	$100.41	9.114%	$109.5614	$109.56	$109.55	$109.60
Purchase #2	$160.28	7.802%	$172.785	$172.79	$172.80	$172.80
Purchase #3	$79.74	12.609%	$89.7944	$89.79	$89.80	$89.80
Purchase #4	$163.50	8.740%	$177.7899	$177.79	$177.80	$177.80
Purchase #5	$203.31	10.244%	$224.1371	$224.14	$224.15	$224.10
Purchase #6	$49.27	5.840%	$52.1474	$52.15	$52.15	$52.10
Purchase #7	$133.53	4.382%	$139.3813	$139.38	$139.40	$139.40
7 purchase totals =	$890.04		$965.5965	$965.60	$965.65	$965.60