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	$200.83	10.721%	$222.361	$222.36	$222.35	$222.40
Purchase #2	$145.38	9.717%	$159.5066	$159.51	$159.50	$159.50
Purchase #3	$84.55	13.752%	$96.1773	$96.18	$96.20	$96.20
Purchase #4	$130.85	6.653%	$139.5555	$139.56	$139.55	$139.60
Purchase #5	$77.99	4.494%	$81.4949	$81.49	$81.50	$81.50
Purchase #6	$42.55	8.246%	$46.0587	$46.06	$46.05	$46.10
Purchase #7	$91.39	13.492%	$103.7203	$103.72	$103.70	$103.70
7 purchase totals =	$773.54		$848.8743	$848.88	$848.85	$849.00