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	$159.74	5.731%	$168.8947	$168.89	$168.90	$168.90
Purchase #2	$66.99	10.577%	$74.0755	$74.08	$74.10	$74.10
Purchase #3	$152.34	12.815%	$171.8624	$171.86	$171.85	$171.90
Purchase #4	$111.89	13.864%	$127.4024	$127.40	$127.40	$127.40
Purchase #5	$191.67	4.810%	$200.8893	$200.89	$200.90	$200.90
Purchase #6	$116.48	13.488%	$132.1908	$132.19	$132.20	$132.20
Purchase #7	$54.45	13.586%	$61.8476	$61.85	$61.85	$61.80
7 purchase totals =	$853.56		$937.1627	$937.16	$937.20	$937.20