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	$132.98	13.260%	$150.6131	$150.61	$150.60	$150.60
Purchase #2	$210.63	6.641%	$224.6179	$224.62	$224.60	$224.60
Purchase #3	$114.98	11.852%	$128.6074	$128.61	$128.60	$128.60
Purchase #4	$55.87	11.600%	$62.3509	$62.35	$62.35	$62.40
Purchase #5	$207.81	10.168%	$228.9401	$228.94	$228.95	$228.90
Purchase #6	$29.61	6.368%	$31.4956	$31.50	$31.50	$31.50
Purchase #7	$229.35	4.200%	$238.9827	$238.98	$239.00	$239.00
7 purchase totals =	$981.23		$1,065.6077	$1,065.61	$1,065.60	$1,065.60