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	$63.51	5.636%	$67.0894	$67.09	$67.10	$67.10
Purchase #2	$164.75	5.825%	$174.3467	$174.35	$174.35	$174.30
Purchase #3	$144.58	4.471%	$151.0442	$151.04	$151.05	$151.00
Purchase #4	$154.49	8.667%	$167.8796	$167.88	$167.90	$167.90
Purchase #5	$7.78	11.335%	$8.6619	$8.66	$8.65	$8.70
Purchase #6	$119.39	10.378%	$131.7803	$131.78	$131.80	$131.80
Purchase #7	$28.76	7.830%	$31.0119	$31.01	$31.00	$31.00
7 purchase totals =	$683.26		$731.8140	$731.81	$731.85	$731.80