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	$233.64	6.313%	$248.3897	$248.39	$248.40	$248.40
Purchase #2	$166.61	9.546%	$182.5146	$182.51	$182.50	$182.50
Purchase #3	$250.72	13.689%	$285.0411	$285.04	$285.05	$285.00
Purchase #4	$62.40	5.676%	$65.9418	$65.94	$65.95	$65.90
Purchase #5	$207.83	8.545%	$225.5891	$225.59	$225.60	$225.60
Purchase #6	$248.88	10.512%	$275.0423	$275.04	$275.05	$275.00
Purchase #7	$225.60	5.501%	$238.0103	$238.01	$238.00	$238.00
7 purchase totals =	$1,395.68		$1,520.5289	$1,520.52	$1,520.55	$1,520.40