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	$134.65	12.748%	$151.8152	$151.82	$151.80	$151.80
Purchase #2	$235.43	3.406%	$243.4487	$243.45	$243.45	$243.40
Purchase #3	$240.94	13.373%	$273.1609	$273.16	$273.15	$273.20
Purchase #4	$132.71	8.319%	$143.7501	$143.75	$143.75	$143.80
Purchase #5	$7.34	4.356%	$7.6597	$7.66	$7.65	$7.70
Purchase #6	$205.43	4.735%	$215.1571	$215.16	$215.15	$215.20
Purchase #7	$42.34	3.380%	$43.7711	$43.77	$43.75	$43.80
7 purchase totals =	$998.84		$1,078.7628	$1,078.77	$1,078.70	$1,078.90