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	$24.31	4.772%	$25.4701	$25.47	$25.45	$25.50
Purchase #2	$85.90	4.225%	$89.5293	$89.53	$89.55	$89.50
Purchase #3	$128.61	12.370%	$144.5191	$144.52	$144.50	$144.50
Purchase #4	$181.25	6.232%	$192.5455	$192.55	$192.55	$192.50
Purchase #5	$207.92	6.658%	$221.7633	$221.76	$221.75	$221.80
Purchase #6	$202.54	10.769%	$224.3515	$224.35	$224.35	$224.40
Purchase #7	$9.88	8.467%	$10.7165	$10.72	$10.70	$10.70
7 purchase totals =	$840.41		$908.8953	$908.90	$908.85	$908.90