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	$246.69	9.168%	$269.3065	$269.31	$269.30	$269.30
Purchase #2	$36.31	5.534%	$38.3194	$38.32	$38.30	$38.30
Purchase #3	$204.65	8.287%	$221.6093	$221.61	$221.60	$221.60
Purchase #4	$189.57	3.636%	$196.4628	$196.46	$196.45	$196.50
Purchase #5	$150.72	6.102%	$159.9169	$159.92	$159.90	$159.90
Purchase #6	$186.57	3.698%	$193.4694	$193.47	$193.45	$193.50
Purchase #7	$10.49	6.787%	$11.202	$11.20	$11.20	$11.20
7 purchase totals =	$1,025.00		$1,090.2863	$1,090.29	$1,090.20	$1,090.30