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	$231.51	3.805%	$240.319	$240.32	$240.30	$240.30
Purchase #2	$72.71	10.690%	$80.4827	$80.48	$80.50	$80.50
Purchase #3	$176.46	5.636%	$186.4053	$186.41	$186.40	$186.40
Purchase #4	$225.75	6.496%	$240.4147	$240.41	$240.40	$240.40
Purchase #5	$204.90	7.827%	$220.9375	$220.94	$220.95	$220.90
Purchase #6	$204.88	8.646%	$222.5939	$222.59	$222.60	$222.60
Purchase #7	$19.86	4.532%	$20.7601	$20.76	$20.75	$20.80
7 purchase totals =	$1,136.07		$1,211.9132	$1,211.91	$1,211.90	$1,211.90