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	$207.43	4.712%	$217.2041	$217.20	$217.20	$217.20
Purchase #2	$148.86	10.215%	$164.066	$164.07	$164.05	$164.10
Purchase #3	$32.32	5.253%	$34.0178	$34.02	$34.00	$34.00
Purchase #4	$99.72	4.757%	$104.4637	$104.46	$104.45	$104.50
Purchase #5	$39.81	7.729%	$42.8869	$42.89	$42.90	$42.90
Purchase #6	$52.49	3.760%	$54.4636	$54.46	$54.45	$54.50
Purchase #7	$48.61	4.469%	$50.7824	$50.78	$50.80	$50.80
7 purchase totals =	$629.24		$667.8845	$667.88	$667.85	$668.00