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	$27.66	5.506%	$29.183	$29.18	$29.20	$29.20
Purchase #2	$57.25	9.196%	$62.5147	$62.51	$62.50	$62.50
Purchase #3	$43.30	5.221%	$45.5607	$45.56	$45.55	$45.60
Purchase #4	$108.94	9.163%	$118.9222	$118.92	$118.90	$118.90
Purchase #5	$113.70	4.138%	$118.4049	$118.40	$118.40	$118.40
Purchase #6	$18.32	11.585%	$20.4424	$20.44	$20.45	$20.40
Purchase #7	$82.74	12.284%	$92.9038	$92.90	$92.90	$92.90
7 purchase totals =	$451.91		$487.9317	$487.91	$487.90	$487.90