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	$106.43	5.410%	$112.1879	$112.19	$112.20	$112.20
Purchase #2	$243.64	4.300%	$254.1165	$254.12	$254.10	$254.10
Purchase #3	$118.90	6.414%	$126.5262	$126.53	$126.55	$126.50
Purchase #4	$19.69	10.586%	$21.7744	$21.77	$21.75	$21.80
Purchase #5	$22.63	6.333%	$24.0632	$24.06	$24.05	$24.10
Purchase #6	$91.75	9.550%	$100.5121	$100.51	$100.50	$100.50
Purchase #7	$139.77	13.520%	$158.6669	$158.67	$158.65	$158.70
7 purchase totals =	$742.81		$797.8472	$797.85	$797.80	$797.90