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	$52.90	12.435%	$59.4781	$59.48	$59.50	$59.50
Purchase #2	$22.48	3.542%	$23.2762	$23.28	$23.30	$23.30
Purchase #3	$190.77	11.295%	$212.3175	$212.32	$212.30	$212.30
Purchase #4	$73.59	13.446%	$83.4849	$83.48	$83.50	$83.50
Purchase #5	$45.75	13.625%	$51.9834	$51.98	$52.00	$52.00
Purchase #6	$138.92	3.545%	$143.8447	$143.84	$143.85	$143.80
Purchase #7	$25.86	10.655%	$28.6154	$28.62	$28.60	$28.60
7 purchase totals =	$550.27		$603.0002	$603.00	$603.05	$603.00