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	$120.27	9.119%	$131.2374	$131.24	$131.25	$131.20
Purchase #2	$163.32	10.224%	$180.0178	$180.02	$180.00	$180.00
Purchase #3	$10.47	6.139%	$11.1128	$11.11	$11.10	$11.10
Purchase #4	$106.40	13.622%	$120.8938	$120.89	$120.90	$120.90
Purchase #5	$34.29	8.162%	$37.0887	$37.09	$37.10	$37.10
Purchase #6	$76.63	11.682%	$85.5819	$85.58	$85.60	$85.60
Purchase #7	$97.37	8.213%	$105.367	$105.37	$105.35	$105.40
7 purchase totals =	$608.75		$671.2994	$671.30	$671.30	$671.30