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	$52.86	5.524%	$55.78	$55.78	$55.80	$55.80
Purchase #2	$131.86	7.675%	$141.9803	$141.98	$142.00	$142.00
Purchase #3	$66.39	11.777%	$74.2088	$74.21	$74.20	$74.20
Purchase #4	$48.39	5.396%	$51.0011	$51.00	$51.00	$51.00
Purchase #5	$33.29	13.690%	$37.8474	$37.85	$37.85	$37.80
Purchase #6	$172.26	5.433%	$181.6189	$181.62	$181.60	$181.60
Purchase #7	$147.31	3.498%	$152.4629	$152.46	$152.45	$152.50
7 purchase totals =	$652.36		$694.8994	$694.90	$694.90	$694.90