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	$134.73	6.433%	$143.3972	$143.40	$143.40	$143.40
Purchase #2	$241.65	10.417%	$266.8227	$266.82	$266.80	$266.80
Purchase #3	$171.43	11.427%	$191.0193	$191.02	$191.00	$191.00
Purchase #4	$173.54	5.368%	$182.8556	$182.86	$182.85	$182.90
Purchase #5	$126.83	11.272%	$141.1263	$141.13	$141.15	$141.10
Purchase #6	$55.54	11.439%	$61.8932	$61.89	$61.90	$61.90
Purchase #7	$39.56	13.247%	$44.8005	$44.80	$44.80	$44.80
7 purchase totals =	$943.28		$1,031.9148	$1,031.92	$1,031.90	$1,031.90