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	$149.77	4.112%	$155.9285	$155.93	$155.95	$155.90
Purchase #2	$248.36	12.846%	$280.2643	$280.26	$280.25	$280.30
Purchase #3	$92.98	13.809%	$105.8196	$105.82	$105.80	$105.80
Purchase #4	$187.49	8.806%	$204.0004	$204.00	$204.00	$204.00
Purchase #5	$92.82	10.689%	$102.7415	$102.74	$102.75	$102.70
Purchase #6	$40.69	4.663%	$42.5874	$42.59	$42.60	$42.60
Purchase #7	$95.49	13.591%	$108.468	$108.47	$108.45	$108.50
7 purchase totals =	$907.60		$999.8097	$999.81	$999.80	$999.80