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	$73.39	9.715%	$80.5198	$80.52	$80.50	$80.50
Purchase #2	$242.28	5.512%	$255.6345	$255.63	$255.65	$255.60
Purchase #3	$17.69	7.746%	$19.0603	$19.06	$19.05	$19.10
Purchase #4	$19.66	6.854%	$21.0075	$21.01	$21.00	$21.00
Purchase #5	$203.56	9.406%	$222.7069	$222.71	$222.70	$222.70
Purchase #6	$117.25	12.333%	$131.7104	$131.71	$131.70	$131.70
Purchase #7	$85.71	12.220%	$96.1838	$96.18	$96.20	$96.20
7 purchase totals =	$759.54		$826.8232	$826.82	$826.80	$826.80