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	$148.36	11.535%	$165.4733	$165.47	$165.45	$165.50
Purchase #2	$226.56	5.381%	$238.7512	$238.75	$238.75	$238.80
Purchase #3	$133.75	4.488%	$139.7527	$139.75	$139.75	$139.80
Purchase #4	$74.45	8.145%	$80.514	$80.51	$80.50	$80.50
Purchase #5	$106.97	10.253%	$117.9376	$117.94	$117.95	$117.90
Purchase #6	$83.50	10.850%	$92.5598	$92.56	$92.55	$92.60
Purchase #7	$46.84	3.499%	$48.4789	$48.48	$48.50	$48.50
7 purchase totals =	$820.43		$883.4675	$883.46	$883.45	$883.60