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	$7.30	11.617%	$8.148	$8.15	$8.15	$8.10
Purchase #2	$27.66	12.104%	$31.008	$31.01	$31.00	$31.00
Purchase #3	$78.92	11.842%	$88.2657	$88.27	$88.25	$88.30
Purchase #4	$117.57	5.111%	$123.579	$123.58	$123.60	$123.60
Purchase #5	$60.71	8.678%	$65.9784	$65.98	$66.00	$66.00
Purchase #6	$149.58	7.332%	$160.5472	$160.55	$160.55	$160.50
Purchase #7	$132.42	8.198%	$143.2758	$143.28	$143.30	$143.30
7 purchase totals =	$574.16		$620.8021	$620.82	$620.85	$620.80