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	$34.58	5.772%	$36.576	$36.58	$36.60	$36.60
Purchase #2	$34.41	12.830%	$38.8248	$38.82	$38.80	$38.80
Purchase #3	$139.48	3.119%	$143.8304	$143.83	$143.85	$143.80
Purchase #4	$54.90	4.405%	$57.3183	$57.32	$57.30	$57.30
Purchase #5	$179.72	10.172%	$198.0011	$198.00	$198.00	$198.00
Purchase #6	$9.52	12.566%	$10.7163	$10.72	$10.70	$10.70
Purchase #7	$64.50	11.541%	$71.9439	$71.94	$71.95	$71.90
7 purchase totals =	$517.11		$557.2108	$557.21	$557.20	$557.10