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	$147.43	4.124%	$153.51	$153.51	$153.50	$153.50
Purchase #2	$105.29	10.178%	$116.0064	$116.01	$116.00	$116.00
Purchase #3	$49.43	11.347%	$55.0388	$55.04	$55.05	$55.00
Purchase #4	$237.74	9.494%	$260.311	$260.31	$260.30	$260.30
Purchase #5	$78.81	4.710%	$82.522	$82.52	$82.50	$82.50
Purchase #6	$70.75	11.646%	$78.9895	$78.99	$79.00	$79.00
Purchase #7	$126.81	8.556%	$137.6599	$137.66	$137.65	$137.70
7 purchase totals =	$816.26		$884.0376	$884.04	$884.00	$884.00