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	$140.49	10.754%	$155.5983	$155.60	$155.60	$155.60
Purchase #2	$98.56	6.731%	$105.1941	$105.19	$105.20	$105.20
Purchase #3	$81.48	10.792%	$90.2733	$90.27	$90.25	$90.30
Purchase #4	$53.32	6.584%	$56.8306	$56.83	$56.85	$56.80
Purchase #5	$96.49	4.135%	$100.4799	$100.48	$100.50	$100.50
Purchase #6	$91.29	11.212%	$101.5254	$101.53	$101.55	$101.50
Purchase #7	$176.82	10.755%	$195.837	$195.84	$195.85	$195.80
7 purchase totals =	$738.45		$805.7386	$805.74	$805.80	$805.70