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	$18.92	10.527%	$20.9117	$20.91	$20.90	$20.90
Purchase #2	$29.83	5.688%	$31.5267	$31.53	$31.55	$31.50
Purchase #3	$87.82	3.490%	$90.8849	$90.88	$90.90	$90.90
Purchase #4	$235.74	3.689%	$244.4364	$244.44	$244.45	$244.40
Purchase #5	$156.71	12.448%	$176.2173	$176.22	$176.20	$176.20
Purchase #6	$31.50	3.671%	$32.6564	$32.66	$32.65	$32.70
Purchase #7	$86.64	3.574%	$89.7365	$89.74	$89.75	$89.70
7 purchase totals =	$647.16		$686.3699	$686.38	$686.40	$686.30