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	$51.69	11.453%	$57.6101	$57.61	$57.60	$57.60
Purchase #2	$30.36	6.102%	$32.2126	$32.21	$32.20	$32.20
Purchase #3	$153.82	3.641%	$159.4206	$159.42	$159.40	$159.40
Purchase #4	$19.41	4.672%	$20.3168	$20.32	$20.30	$20.30
Purchase #5	$29.79	12.571%	$33.5349	$33.53	$33.55	$33.50
Purchase #6	$194.59	8.108%	$210.3674	$210.37	$210.35	$210.40
Purchase #7	$98.80	4.373%	$103.1205	$103.12	$103.10	$103.10
7 purchase totals =	$578.46		$616.5829	$616.58	$616.50	$616.50