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	$24.74	10.696%	$27.3862	$27.39	$27.40	$27.40
Purchase #2	$188.45	3.259%	$194.5916	$194.59	$194.60	$194.60
Purchase #3	$167.52	6.840%	$178.9784	$178.98	$179.00	$179.00
Purchase #4	$179.41	11.511%	$200.0619	$200.06	$200.05	$200.10
Purchase #5	$233.27	10.218%	$257.1055	$257.11	$257.10	$257.10
Purchase #6	$207.90	6.817%	$222.0725	$222.07	$222.05	$222.10
Purchase #7	$54.25	5.262%	$57.1046	$57.10	$57.10	$57.10
7 purchase totals =	$1,055.54		$1,137.3007	$1,137.30	$1,137.30	$1,137.40