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	$50.68	9.295%	$55.3907	$55.39	$55.40	$55.40
Purchase #2	$13.60	5.317%	$14.3231	$14.32	$14.30	$14.30
Purchase #3	$10.25	3.489%	$10.6076	$10.61	$10.60	$10.60
Purchase #4	$30.64	6.116%	$32.5139	$32.51	$32.50	$32.50
Purchase #5	$200.38	10.423%	$221.2656	$221.27	$221.25	$221.30
Purchase #6	$188.26	11.765%	$210.4088	$210.41	$210.40	$210.40
Purchase #7	$90.57	8.400%	$98.1779	$98.18	$98.20	$98.20
7 purchase totals =	$584.38		$642.6876	$642.69	$642.65	$642.70