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	$120.99	10.386%	$133.556	$133.56	$133.55	$133.60
Purchase #2	$87.88	8.456%	$95.3111	$95.31	$95.30	$95.30
Purchase #3	$70.40	10.539%	$77.8195	$77.82	$77.80	$77.80
Purchase #4	$241.92	5.661%	$255.6151	$255.62	$255.60	$255.60
Purchase #5	$69.73	12.566%	$78.4923	$78.49	$78.50	$78.50
Purchase #6	$87.39	10.221%	$96.3221	$96.32	$96.30	$96.30
Purchase #7	$178.44	6.516%	$190.0672	$190.07	$190.05	$190.10
7 purchase totals =	$856.75		$927.1833	$927.19	$927.10	$927.20