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	$249.67	4.827%	$261.7216	$261.72	$261.70	$261.70
Purchase #2	$168.43	11.316%	$187.4895	$187.49	$187.50	$187.50
Purchase #3	$30.30	3.749%	$31.4359	$31.44	$31.45	$31.40
Purchase #4	$249.40	10.861%	$276.4873	$276.49	$276.50	$276.50
Purchase #5	$231.83	10.260%	$255.6158	$255.62	$255.60	$255.60
Purchase #6	$45.73	3.506%	$47.3333	$47.33	$47.35	$47.30
Purchase #7	$34.61	12.370%	$38.8913	$38.89	$38.90	$38.90
7 purchase totals =	$1,009.97		$1,098.9747	$1,098.98	$1,099.00	$1,098.90