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	$153.30	13.753%	$174.3833	$174.38	$174.40	$174.40
Purchase #2	$61.79	8.285%	$66.9093	$66.91	$66.90	$66.90
Purchase #3	$246.98	7.632%	$265.8295	$265.83	$265.85	$265.80
Purchase #4	$43.35	10.846%	$48.0517	$48.05	$48.05	$48.10
Purchase #5	$220.41	9.718%	$241.8294	$241.83	$241.85	$241.80
Purchase #6	$44.31	13.705%	$50.3827	$50.38	$50.40	$50.40
Purchase #7	$174.96	7.218%	$187.5886	$187.59	$187.60	$187.60
7 purchase totals =	$945.10		$1,034.9745	$1,034.97	$1,035.05	$1,035.00