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	$78.35	4.767%	$82.0849	$82.08	$82.10	$82.10
Purchase #2	$79.98	7.401%	$85.8993	$85.90	$85.90	$85.90
Purchase #3	$146.52	8.205%	$158.542	$158.54	$158.55	$158.50
Purchase #4	$70.91	10.176%	$78.1258	$78.13	$78.15	$78.10
Purchase #5	$171.30	11.252%	$190.5747	$190.57	$190.55	$190.60
Purchase #6	$13.79	5.721%	$14.5789	$14.58	$14.60	$14.60
Purchase #7	$25.48	8.144%	$27.5551	$27.56	$27.55	$27.60
7 purchase totals =	$586.33		$637.3607	$637.36	$637.40	$637.40