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	$82.81	7.273%	$88.8328	$88.83	$88.85	$88.80
Purchase #2	$62.39	5.144%	$65.5993	$65.60	$65.60	$65.60
Purchase #3	$78.58	6.507%	$83.6932	$83.69	$83.70	$83.70
Purchase #4	$129.75	11.790%	$145.0475	$145.05	$145.05	$145.00
Purchase #5	$88.62	8.305%	$95.9799	$95.98	$96.00	$96.00
Purchase #6	$30.46	6.293%	$32.3768	$32.38	$32.40	$32.40
Purchase #7	$121.25	5.545%	$127.9733	$127.97	$127.95	$128.00
7 purchase totals =	$593.86		$639.5028	$639.50	$639.55	$639.50