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	$249.89	12.425%	$280.9388	$280.94	$280.95	$280.90
Purchase #2	$143.51	6.222%	$152.4392	$152.44	$152.45	$152.40
Purchase #3	$150.51	5.806%	$159.2486	$159.25	$159.25	$159.20
Purchase #4	$48.94	5.625%	$51.6929	$51.69	$51.70	$51.70
Purchase #5	$245.25	11.472%	$273.3851	$273.39	$273.40	$273.40
Purchase #6	$203.97	11.656%	$227.7447	$227.74	$227.75	$227.70
Purchase #7	$81.69	9.587%	$89.5216	$89.52	$89.50	$89.50
7 purchase totals =	$1,123.76		$1,234.9709	$1,234.97	$1,235.00	$1,234.80