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	$239.88	6.798%	$256.187	$256.19	$256.20	$256.20
Purchase #2	$48.81	12.118%	$54.7248	$54.72	$54.70	$54.70
Purchase #3	$160.51	7.456%	$172.4776	$172.48	$172.50	$172.50
Purchase #4	$211.25	5.807%	$223.5173	$223.52	$223.50	$223.50
Purchase #5	$27.92	4.661%	$29.2214	$29.22	$29.20	$29.20
Purchase #6	$80.76	8.253%	$87.4251	$87.43	$87.45	$87.40
Purchase #7	$181.83	7.759%	$195.9382	$195.94	$195.95	$195.90
7 purchase totals =	$950.96		$1,019.4914	$1,019.50	$1,019.50	$1,019.40