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	$230.69	8.516%	$250.3356	$250.34	$250.35	$250.30
Purchase #2	$52.48	13.777%	$59.7102	$59.71	$59.70	$59.70
Purchase #3	$131.37	9.455%	$143.791	$143.79	$143.80	$143.80
Purchase #4	$90.57	11.199%	$100.7129	$100.71	$100.70	$100.70
Purchase #5	$243.43	3.760%	$252.583	$252.58	$252.60	$252.60
Purchase #6	$210.99	7.307%	$226.407	$226.41	$226.40	$226.40
Purchase #7	$41.59	13.537%	$47.22	$47.22	$47.20	$47.20
7 purchase totals =	$1,001.12		$1,080.7597	$1,080.76	$1,080.75	$1,080.70