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	$234.55	12.509%	$263.8899	$263.89	$263.90	$263.90
Purchase #2	$170.91	11.102%	$189.8844	$189.88	$189.90	$189.90
Purchase #3	$52.82	12.398%	$59.3686	$59.37	$59.35	$59.40
Purchase #4	$53.72	10.216%	$59.208	$59.21	$59.20	$59.20
Purchase #5	$128.69	3.686%	$133.4335	$133.43	$133.45	$133.40
Purchase #6	$57.80	9.851%	$63.4939	$63.49	$63.50	$63.50
Purchase #7	$21.55	8.732%	$23.4317	$23.43	$23.45	$23.40
7 purchase totals =	$720.04		$792.7100	$792.70	$792.75	$792.70