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	$94.70	5.433%	$99.8451	$99.85	$99.85	$99.80
Purchase #2	$233.54	9.534%	$255.8057	$255.81	$255.80	$255.80
Purchase #3	$49.82	9.338%	$54.4722	$54.47	$54.45	$54.50
Purchase #4	$39.81	7.155%	$42.6584	$42.66	$42.65	$42.70
Purchase #5	$145.62	5.190%	$153.1777	$153.18	$153.20	$153.20
Purchase #6	$57.91	10.224%	$63.8307	$63.83	$63.85	$63.80
Purchase #7	$8.44	5.253%	$8.8834	$8.88	$8.90	$8.90
7 purchase totals =	$629.84		$678.6732	$678.68	$678.70	$678.70