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	$140.86	12.105%	$157.9111	$157.91	$157.90	$157.90
Purchase #2	$73.90	4.144%	$76.9624	$76.96	$76.95	$77.00
Purchase #3	$90.40	11.335%	$100.6468	$100.65	$100.65	$100.60
Purchase #4	$158.50	12.807%	$178.7991	$178.80	$178.80	$178.80
Purchase #5	$141.74	4.665%	$148.3522	$148.35	$148.35	$148.40
Purchase #6	$62.93	11.780%	$70.3432	$70.34	$70.35	$70.30
Purchase #7	$247.56	13.343%	$280.5919	$280.59	$280.60	$280.60
7 purchase totals =	$915.89		$1,013.6067	$1,013.60	$1,013.60	$1,013.60