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	$129.78	5.737%	$137.2255	$137.23	$137.25	$137.20
Purchase #2	$98.25	5.564%	$103.7166	$103.72	$103.70	$103.70
Purchase #3	$47.51	13.185%	$53.7742	$53.77	$53.75	$53.80
Purchase #4	$109.63	8.641%	$119.1031	$119.10	$119.10	$119.10
Purchase #5	$158.40	3.820%	$164.4509	$164.45	$164.45	$164.50
Purchase #6	$240.95	7.861%	$259.8911	$259.89	$259.90	$259.90
Purchase #7	$131.59	7.823%	$141.8843	$141.88	$141.90	$141.90
7 purchase totals =	$916.11		$980.0457	$980.04	$980.05	$980.10