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	$125.39	13.111%	$141.8299	$141.83	$141.85	$141.80
Purchase #2	$197.26	3.487%	$204.1385	$204.14	$204.15	$204.10
Purchase #3	$96.73	6.510%	$103.0271	$103.03	$103.05	$103.00
Purchase #4	$49.74	4.202%	$51.8301	$51.83	$51.85	$51.80
Purchase #5	$33.78	9.586%	$37.0182	$37.02	$37.00	$37.00
Purchase #6	$141.69	4.599%	$148.2063	$148.21	$148.20	$148.20
Purchase #7	$86.30	3.708%	$89.5	$89.50	$89.50	$89.50
7 purchase totals =	$730.89		$775.5501	$775.56	$775.60	$775.40