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	$29.73	4.296%	$31.0072	$31.01	$31.00	$31.00
Purchase #2	$60.88	9.158%	$66.4554	$66.46	$66.45	$66.50
Purchase #3	$31.32	3.743%	$32.4923	$32.49	$32.50	$32.50
Purchase #4	$227.73	11.584%	$254.1102	$254.11	$254.10	$254.10
Purchase #5	$52.56	8.150%	$56.8436	$56.84	$56.85	$56.80
Purchase #6	$12.76	4.716%	$13.3618	$13.36	$13.35	$13.40
Purchase #7	$47.88	3.579%	$49.5936	$49.59	$49.60	$49.60
7 purchase totals =	$462.86		$503.8641	$503.86	$503.85	$503.90