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	$237.78	7.854%	$256.4552	$256.46	$256.45	$256.50
Purchase #2	$88.55	6.686%	$94.4705	$94.47	$94.45	$94.50
Purchase #3	$116.56	9.417%	$127.5365	$127.54	$127.55	$127.50
Purchase #4	$29.55	8.792%	$32.148	$32.15	$32.15	$32.10
Purchase #5	$115.62	5.206%	$121.6392	$121.64	$121.65	$121.60
Purchase #6	$127.32	3.741%	$132.083	$132.08	$132.10	$132.10
Purchase #7	$5.68	9.683%	$6.23	$6.23	$6.25	$6.20
7 purchase totals =	$721.06		$770.5624	$770.57	$770.60	$770.50