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	$31.76	4.825%	$33.2924	$33.29	$33.30	$33.30
Purchase #2	$250.40	6.207%	$265.9423	$265.94	$265.95	$265.90
Purchase #3	$175.94	9.218%	$192.1581	$192.16	$192.15	$192.20
Purchase #4	$90.96	10.374%	$100.3962	$100.40	$100.40	$100.40
Purchase #5	$60.49	9.262%	$66.0926	$66.09	$66.10	$66.10
Purchase #6	$52.91	12.724%	$59.6423	$59.64	$59.65	$59.60
Purchase #7	$38.43	10.158%	$42.3337	$42.33	$42.35	$42.30
7 purchase totals =	$700.89		$759.8576	$759.85	$759.90	$759.80