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	$189.29	5.699%	$200.0776	$200.08	$200.10	$200.10
Purchase #2	$174.90	12.372%	$196.5386	$196.54	$196.55	$196.50
Purchase #3	$176.40	11.266%	$196.2732	$196.27	$196.25	$196.30
Purchase #4	$82.72	7.183%	$88.6618	$88.66	$88.65	$88.70
Purchase #5	$132.82	9.164%	$144.9916	$144.99	$145.00	$145.00
Purchase #6	$237.86	11.611%	$265.4779	$265.48	$265.50	$265.50
Purchase #7	$58.96	10.612%	$65.2168	$65.22	$65.20	$65.20
7 purchase totals =	$1,052.95		$1,157.2375	$1,157.24	$1,157.25	$1,157.30