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	$134.53	3.866%	$139.7309	$139.73	$139.75	$139.70
Purchase #2	$138.48	10.518%	$153.0453	$153.05	$153.05	$153.00
Purchase #3	$150.89	11.620%	$168.4234	$168.42	$168.40	$168.40
Purchase #4	$171.60	9.696%	$188.2383	$188.24	$188.25	$188.20
Purchase #5	$80.56	13.311%	$91.2833	$91.28	$91.30	$91.30
Purchase #6	$250.93	3.224%	$259.02	$259.02	$259.00	$259.00
Purchase #7	$86.86	3.202%	$89.6413	$89.64	$89.65	$89.60
7 purchase totals =	$1,013.85		$1,089.3825	$1,089.38	$1,089.40	$1,089.20