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	$151.61	13.339%	$171.8333	$171.83	$171.85	$171.80
Purchase #2	$99.30	6.107%	$105.3643	$105.36	$105.35	$105.40
Purchase #3	$96.30	5.553%	$101.6475	$101.65	$101.65	$101.60
Purchase #4	$167.71	3.695%	$173.9069	$173.91	$173.90	$173.90
Purchase #5	$29.39	5.523%	$31.0132	$31.01	$31.00	$31.00
Purchase #6	$61.95	10.606%	$68.5204	$68.52	$68.50	$68.50
Purchase #7	$11.34	9.249%	$12.3888	$12.39	$12.40	$12.40
7 purchase totals =	$617.60		$664.6744	$664.67	$664.65	$664.60