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	$99.43	13.539%	$112.8918	$112.89	$112.90	$112.90
Purchase #2	$111.72	10.786%	$123.7701	$123.77	$123.75	$123.80
Purchase #3	$30.98	3.662%	$32.1145	$32.11	$32.10	$32.10
Purchase #4	$212.79	5.682%	$224.8807	$224.88	$224.90	$224.90
Purchase #5	$32.85	4.871%	$34.4501	$34.45	$34.45	$34.50
Purchase #6	$185.51	11.738%	$207.2852	$207.29	$207.30	$207.30
Purchase #7	$57.50	12.865%	$64.8974	$64.90	$64.90	$64.90
7 purchase totals =	$730.78		$800.2898	$800.29	$800.30	$800.40