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	$200.25	7.176%	$214.6199	$214.62	$214.60	$214.60
Purchase #2	$170.30	8.713%	$185.1382	$185.14	$185.15	$185.10
Purchase #3	$52.36	13.643%	$59.5035	$59.50	$59.50	$59.50
Purchase #4	$19.84	4.403%	$20.7136	$20.71	$20.70	$20.70
Purchase #5	$163.67	4.259%	$170.6407	$170.64	$170.65	$170.60
Purchase #6	$42.75	11.172%	$47.526	$47.53	$47.55	$47.50
Purchase #7	$125.69	12.564%	$141.4817	$141.48	$141.50	$141.50
7 purchase totals =	$774.86		$839.6236	$839.62	$839.65	$839.50