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	$92.89	7.710%	$100.0518	$100.05	$100.05	$100.10
Purchase #2	$155.41	8.150%	$168.0759	$168.08	$168.10	$168.10
Purchase #3	$214.50	6.639%	$228.7407	$228.74	$228.75	$228.70
Purchase #4	$105.75	7.267%	$113.4349	$113.43	$113.45	$113.40
Purchase #5	$56.27	5.783%	$59.5241	$59.52	$59.50	$59.50
Purchase #6	$117.86	6.255%	$125.2321	$125.23	$125.25	$125.20
Purchase #7	$86.30	3.683%	$89.4784	$89.48	$89.50	$89.50
7 purchase totals =	$828.98		$884.5379	$884.53	$884.60	$884.50