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	$115.28	7.410%	$123.8222	$123.82	$123.80	$123.80
Purchase #2	$106.25	5.823%	$112.4369	$112.44	$112.45	$112.40
Purchase #3	$92.94	11.123%	$103.2777	$103.28	$103.30	$103.30
Purchase #4	$177.51	3.705%	$184.0867	$184.09	$184.10	$184.10
Purchase #5	$134.52	8.490%	$145.9407	$145.94	$145.95	$145.90
Purchase #6	$168.73	11.133%	$187.5147	$187.51	$187.50	$187.50
Purchase #7	$120.38	6.473%	$128.1722	$128.17	$128.15	$128.20
7 purchase totals =	$915.61		$985.2511	$985.25	$985.25	$985.20