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	$26.65	7.151%	$28.5557	$28.56	$28.55	$28.60
Purchase #2	$119.67	4.255%	$124.762	$124.76	$124.75	$124.80
Purchase #3	$82.56	8.717%	$89.7568	$89.76	$89.75	$89.80
Purchase #4	$233.28	9.474%	$255.3809	$255.38	$255.40	$255.40
Purchase #5	$243.93	7.363%	$261.8906	$261.89	$261.90	$261.90
Purchase #6	$111.51	10.338%	$123.0379	$123.04	$123.05	$123.00
Purchase #7	$73.62	12.103%	$82.5302	$82.53	$82.55	$82.50
7 purchase totals =	$891.22		$965.9141	$965.92	$965.95	$966.00