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	$225.72	10.503%	$249.4274	$249.43	$249.45	$249.40
Purchase #2	$236.71	9.709%	$259.6922	$259.69	$259.70	$259.70
Purchase #3	$92.88	8.359%	$100.6438	$100.64	$100.65	$100.60
Purchase #4	$128.73	12.810%	$145.2203	$145.22	$145.20	$145.20
Purchase #5	$69.34	3.451%	$71.7329	$71.73	$71.75	$71.70
Purchase #6	$88.47	13.829%	$100.7045	$100.70	$100.70	$100.70
Purchase #7	$69.59	12.606%	$78.3625	$78.36	$78.35	$78.40
7 purchase totals =	$911.44		$1,005.7836	$1,005.77	$1,005.80	$1,005.70