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	$59.56	8.847%	$64.8293	$64.83	$64.85	$64.80
Purchase #2	$173.61	8.539%	$188.4346	$188.43	$188.45	$188.40
Purchase #3	$35.63	8.397%	$38.6219	$38.62	$38.60	$38.60
Purchase #4	$235.29	6.635%	$250.9015	$250.90	$250.90	$250.90
Purchase #5	$103.66	12.677%	$116.801	$116.80	$116.80	$116.80
Purchase #6	$47.83	7.749%	$51.5363	$51.54	$51.55	$51.50
Purchase #7	$81.63	4.131%	$85.0021	$85.00	$85.00	$85.00
7 purchase totals =	$737.21		$796.1267	$796.12	$796.15	$796.00