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	$137.30	5.111%	$144.3174	$144.32	$144.30	$144.30
Purchase #2	$114.37	5.119%	$120.2246	$120.22	$120.20	$120.20
Purchase #3	$54.35	8.780%	$59.1219	$59.12	$59.10	$59.10
Purchase #4	$197.97	5.230%	$208.3238	$208.32	$208.30	$208.30
Purchase #5	$42.90	9.536%	$46.9909	$46.99	$47.00	$47.00
Purchase #6	$48.89	6.731%	$52.1808	$52.18	$52.20	$52.20
Purchase #7	$178.72	3.173%	$184.3908	$184.39	$184.40	$184.40
7 purchase totals =	$774.50		$815.5502	$815.54	$815.50	$815.50