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	$238.29	13.399%	$270.2185	$270.22	$270.20	$270.20
Purchase #2	$185.44	7.424%	$199.2071	$199.21	$199.20	$199.20
Purchase #3	$247.45	3.356%	$255.7544	$255.75	$255.75	$255.80
Purchase #4	$26.51	13.536%	$30.0984	$30.10	$30.10	$30.10
Purchase #5	$199.57	11.710%	$222.9396	$222.94	$222.95	$222.90
Purchase #6	$62.81	9.775%	$68.9497	$68.95	$68.95	$68.90
Purchase #7	$50.29	6.314%	$53.4653	$53.47	$53.45	$53.50
7 purchase totals =	$1,010.36		$1,100.6330	$1,100.64	$1,100.60	$1,100.60