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	$73.82	4.295%	$76.9906	$76.99	$77.00	$77.00
Purchase #2	$153.50	10.427%	$169.5054	$169.51	$169.50	$169.50
Purchase #3	$94.67	12.574%	$106.5738	$106.57	$106.55	$106.60
Purchase #4	$28.62	9.431%	$31.3192	$31.32	$31.30	$31.30
Purchase #5	$68.91	8.360%	$74.6709	$74.67	$74.65	$74.70
Purchase #6	$80.53	12.116%	$90.287	$90.29	$90.30	$90.30
Purchase #7	$82.47	9.444%	$90.2585	$90.26	$90.25	$90.30
7 purchase totals =	$582.52		$639.6054	$639.61	$639.55	$639.70