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	$70.41	3.784%	$73.0743	$73.07	$73.05	$73.10
Purchase #2	$94.29	5.162%	$99.1572	$99.16	$99.15	$99.20
Purchase #3	$227.72	13.209%	$257.7995	$257.80	$257.80	$257.80
Purchase #4	$43.95	5.384%	$46.3163	$46.32	$46.30	$46.30
Purchase #5	$245.77	9.200%	$268.3808	$268.38	$268.40	$268.40
Purchase #6	$38.70	4.246%	$40.3432	$40.34	$40.35	$40.30
Purchase #7	$246.96	3.558%	$255.7468	$255.75	$255.75	$255.70
7 purchase totals =	$967.80		$1,040.8181	$1,040.82	$1,040.80	$1,040.80