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	$89.32	12.466%	$100.4546	$100.45	$100.45	$100.50
Purchase #2	$154.38	13.707%	$175.5409	$175.54	$175.55	$175.50
Purchase #3	$229.98	9.259%	$251.2738	$251.27	$251.25	$251.30
Purchase #4	$192.96	4.567%	$201.7725	$201.77	$201.75	$201.80
Purchase #5	$223.70	11.128%	$248.5933	$248.59	$248.60	$248.60
Purchase #6	$79.60	7.349%	$85.4498	$85.45	$85.45	$85.40
Purchase #7	$25.52	6.595%	$27.203	$27.20	$27.20	$27.20
7 purchase totals =	$995.46		$1,090.2879	$1,090.27	$1,090.25	$1,090.30