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	$229.77	8.102%	$248.386	$248.39	$248.40	$248.40
Purchase #2	$36.96	13.430%	$41.9237	$41.92	$41.90	$41.90
Purchase #3	$156.80	5.349%	$165.1872	$165.19	$165.20	$165.20
Purchase #4	$10.47	4.453%	$10.9362	$10.94	$10.95	$10.90
Purchase #5	$71.84	9.404%	$78.5958	$78.60	$78.60	$78.60
Purchase #6	$215.34	7.673%	$231.863	$231.86	$231.85	$231.90
Purchase #7	$118.74	12.228%	$133.2595	$133.26	$133.25	$133.30
7 purchase totals =	$839.92		$910.1514	$910.16	$910.15	$910.20