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	$71.66	12.450%	$80.5817	$80.58	$80.60	$80.60
Purchase #2	$30.69	9.811%	$33.701	$33.70	$33.70	$33.70
Purchase #3	$109.88	11.620%	$122.6481	$122.65	$122.65	$122.60
Purchase #4	$32.84	13.736%	$37.3509	$37.35	$37.35	$37.40
Purchase #5	$215.82	12.705%	$243.2399	$243.24	$243.25	$243.20
Purchase #6	$48.45	10.436%	$53.5062	$53.51	$53.50	$53.50
Purchase #7	$116.54	9.616%	$127.7465	$127.75	$127.75	$127.70
7 purchase totals =	$625.88		$698.7743	$698.78	$698.80	$698.70