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	$72.31	8.422%	$78.3999	$78.40	$78.40	$78.40
Purchase #2	$147.50	12.143%	$165.4109	$165.41	$165.40	$165.40
Purchase #3	$19.83	13.127%	$22.4331	$22.43	$22.45	$22.40
Purchase #4	$35.46	6.249%	$37.6759	$37.68	$37.70	$37.70
Purchase #5	$84.87	5.288%	$89.3579	$89.36	$89.35	$89.40
Purchase #6	$121.82	12.667%	$137.2509	$137.25	$137.25	$137.30
Purchase #7	$95.78	13.797%	$108.9948	$108.99	$109.00	$109.00
7 purchase totals =	$577.57		$639.5234	$639.52	$639.55	$639.60